that

[th at; unstressed th uh t] /ðæt; unstressed ðət/
pronoun, plural those.
1.
(used to indicate a person, thing, idea, state, event, time, remark, etc., as pointed out or present, mentioned before, supposed to be understood, or by way of emphasis):
That is her mother. After that we saw each other.
2.
(used to indicate one of two or more persons, things, etc., already mentioned, referring to the one more remote in place, time, or thought; opposed to this):
This is my sister and that's my cousin.
3.
(used to indicate one of two or more persons, things, etc., already mentioned, implying a contrast or contradistinction; opposed to this):
This suit fits better than that.
4.
(used as the subject or object of a relative clause, especially one defining or restricting the antecedent, sometimes replaceable by who, whom, or which):
the horse that he bought.
5.
(used as the object of a preposition, with the preposition standing at the end of a relative clause):
the farm that I spoke of.
6.
(used in various special or elliptical constructions):
fool that he is.
adjective, plural those.
7.
(used to indicate a person, place, thing, or degree as indicated, mentioned before, present, or as well-known or characteristic):
That woman is her mother. Those little mannerisms of hers make me sick.
8.
(used to indicate the more remote in time, place, or thought of two persons, things, etc., already mentioned; opposed to this):
This room is his and that one is mine.
9.
(used to imply mere contradistinction; opposed to this):
not this house, but that one.
adverb
10.
(used with adjectives and adverbs of quantity or extent) to the extent or degree indicated:
that much; The fish was that big.
11.
to a great extent or degree; very:
It's not that important.
12.
Dialect. (used to modify an adjective or another adverb) to such an extent:
He was that weak he could hardly stand.
conjunction
13.
(used to introduce a subordinate clause as the subject or object of the principal verb or as the necessary complement to a statement made, or a clause expressing cause or reason, purpose or aim, result or consequence, etc.):
I'm sure that you'll like it. That he will come is certain. Hold it up so that everyone can see it.
14.
(used elliptically to introduce an exclamation expressing desire, a wish, surprise, indignation, or other strong feeling):
Oh, that I had never been born!
Idioms
15.
at that,
  1. in spite of something; nevertheless:
    Although perhaps too elaborate, it seemed like a good plan at that.
  2. in addition; besides:
    It was a long wait, and an exasperating one at that.
16.
that is, (by way of explanation, clarification, or an example); more accurately: I read the book, that is, I read most of it.
I believe his account of the story, that is to say, I have no reason to doubt it.
Also, that is to say.
17.
that's that, Informal. there is no more to be said or done; that is finished:
I'm not going, and that's that!
18.
that way, Informal. in love or very fond of (usually followed by about or for):
The star and the director are that way. I'm that way about coffee.
19.
with that, following that; thereupon:
With that, he turned on his heel and fled.
Origin
before 900; Middle English; Old English thæt (pronoun, adj., adv. and conjunction), orig., neuter of se the; cognate with Dutch dat, German das(s), Old Norse that, Greek tó, Sanskrit tad
Can be confused
that, which (see usage note at the current entry)
Usage note
4. When that introduces a relative clause, the clause is usually restrictive; that is, essential to the complete meaning of the sentence because it restricts or specifies the noun or pronoun it modifies. In the sentence The keys that I lost last month have been found, it is clear that keys referred to are a particular set. Without the that clause, the sentence The keys have been found would be vague and probably puzzling. That is used to refer to animate and inanimate nouns and thus can substitute in most uses for who(m) and which: Many of the workers that (or who) built the pyramids died while working. The negotiator made an offer that (or which) was very attractive to the union. Experienced writers choose among these forms not only on the basis of grammar and the kind of noun referred to but also on the basis of sound of the sentence and their own personal preference.
The relative pronoun that is sometimes omitted. Its omission as a subject is usually considered nonstandard, but the construction is heard occasionally even from educated speakers: A fellow (that) lives near here takes people rafting. Most often it is as an object that the relative pronoun is omitted. The omission almost always occurs when the dependent clause begins with a personal pronoun or a proper name: The mechanic (that) we take our car to is very competent. The films (that) Chaplin made have become classics. The omission of the relative pronoun as in the two preceding examples is standard in all varieties of speech and writing.
13. The conjunction that, which introduces a noun clause, is, like the relative pronoun that, sometimes omitted, often after verbs of thinking, saying, believing, etc.: She said (that) they would come in separate cars. He dismissed the idea (that) he was being followed. As with the omission of the relative pronoun, the omission of the conjunction almost always occurs when the dependent clause begins with a personal pronoun or with a proper name. This omission of the conjunction that occurs most frequently in informal speech and writing, but it is a stylistic option often chosen in more formal speech and writing.

that's

[th ats; unstressed th uh ts] /ðæts; unstressed ðəts/
1.
contraction of that is:
That's mine.
2.
contraction of that has:
That's got more leaves.
Usage note
Examples from the web for that
  • Let's say you want to identify the mold on that leftover pizza.
  • Squaring many circles:An ambitious single currency depended on a fiscal rule book that was never followed.
  • Cats and failures highlight this list of the memes that have gone mainstream.
  • New research shows that, unlike cigarettes, smoking marijuana from time to time may even increase lung airflow rates and capacity.
  • Doctors long believed that patients who remained in a coma weeks or more after a brain injury would never regain consciousness.
  • Bed bugs are a nuisance that is on the rise around the world, but the bugs don't spread disease, according to new research.
  • It is often in the excuses and in the apologies that one finds the real offense.
  • Windows that absorb or reflect light and heat at the flick of a switch could help cut heating and cooling bills.
British Dictionary definitions for that

that

/ðæt; unstressed ðət/
determiner (used before a sing noun)
1.
  1. used preceding a noun that has been mentioned at some time or is understood: that idea of yours
  2. (as pronoun): don't eat that, that's what I mean
2.
  1. used preceding a noun that denotes something more remote or removed: that dress is cheaper than this one, that building over there is for sale
  2. (as pronoun): that is John and this is his wife, give me that Compare this
3.
used to refer to something that is familiar: that old chap from across the street
4.
(informal) and that, and all that, everything connected with the subject mentioned: he knows a lot about building and that
5.
(completive-intensive) at that, additionally, all things considered, or nevertheless: he's a pleasant fellow at that, I might decide to go at that
6.
like that
  1. with ease; effortlessly: he gave me the answer just like that
  2. of such a nature, character, etc: he paid for all our tickets — he's like that
7.
that is
  1. to be precise
  2. in other words
  3. for example
8.
that's more like it, that is better, an improvement, etc
9.
that's that, there is no more to be done, discussed, etc
10.
with that, at that, thereupon; having said or done that
conjunction (subordinating)
11.
used to introduce a noun clause: I believe that you'll come
12.
Also so that, in order that. used to introduce a clause of purpose: they fought that others might have peace
13.
used to introduce a clause of result: he laughed so hard that he cried
14.
used to introduce a clause after an understood sentence expressing desire, indignation, or amazement: oh, that I had never lived!
adverb
15.
used with adjectives or adverbs to reinforce the specification of a precise degree already mentioned: go just that fast and you should be safe
16.
(usually used with a negative) (informal) Also all that. (intensifier): he wasn't that upset at the news
17.
(dialect) (intensifier): the cat was that weak after the fight
pronoun
18.
used to introduce a restrictive relative clause: the book that we want
19.
used to introduce a clause with the verb to be to emphasize the extent to which the preceding noun is applicable: genius that she is, she outwitted the computer
Usage note
Precise stylists maintain a distinction between that and which: that is used as a relative pronoun in restrictive clauses and which in nonrestrictive clauses. In the book that is on the table is mine, the clause that is on the table is used to distinguish one particular book (the one on the table) from another or others (which may be anywhere, but not on the table). In the book, which is on the table, is mine, the which clause is merely descriptive or incidental. The more formal the level of language, the more important it is to preserve the distinction between the two relative pronouns; but in informal or colloquial usage, the words are often used interchangeably
Word Origin
Old English thæt; related to Old Frisian thet, Old Norse, Old Saxon that, Old High German daz, Greek to, Latin istud, Sanskrit tad
Word Origin and History for that
pron.

Old English þæt, neuter singular of the demonstrative pronoun and adjective (corresponding to masc. se, fem. seo), from Proto-Germanic *that, from PIE *tod-, extended form of demonstrative pronomial base *to- (cf. Sanskrit ta-, Lithuanian and Old Church Slavonic to, Greek to "the," Latin talis "such"). Cf. the.

Emerged c.1200 as a demonstrative adjective with the breakdown of the Old English grammatical gender system, perhaps by influence of French and Latin, which had demonstrative adjectives (Old English did not). Slang that way "in love" first recorded 1929. That-a-way is recorded from 1839. "Take that!" said while delivering a blow, is recorded from early 15c.

Idioms and Phrases with that