-ic

1.
a suffix forming adjectives from other parts of speech, occurring originally in Greek and Latin loanwords (metallic; poetic; archaic; public) and, on this model, used as an adjective-forming suffix with the particular senses “having some characteristics of” (opposed to the simple attributive use of the base noun) (balletic; sophomoric); “in the style of” (Byronic; Miltonic); “pertaining to a family of peoples or languages” (Finnic; Semitic; Turkic).
2.
Chemistry. a suffix, specialized in opposition to -ous, used to show the higher of two valences:
ferric chloride.
3.
a noun suffix occurring chiefly in loanwords from Greek, where such words were originally adjectival (critic; magic; music).
Origin
Middle English -ic, -ik < Latin -icus; in many words representing the cognate Greek -ikos (directly or through L); in some words replacing -ique < French < Latin -icus
British Dictionary definitions for -ic

-ic

suffix
1.
of, relating to, or resembling: allergic, Germanic, periodic See also -ical
2.
(in chemistry) indicating that an element is chemically combined in the higher of two possible valence states: ferric, stannic Compare -ous (sense 2)
Word Origin
from Latin -icus or Greek -ikos; -ic also occurs in nouns that represent a substantive use of adjectives (magic) and in nouns borrowed directly from Latin or Greek (critic, music)
Word Origin and History for -ic

adjective suffix, "having to do with, having the nature of, being, made of, caused by, similar to" (in chemistry, indicating a higher valence than names in -ous), from French -ique and directly from Latin -icus, which in many cases represents Greek -ikos "in the manner of; pertaining to." From PIE *-(i)ko, which also yielded Slavic -isku, adjectival suffix indicating origin, the source of the -sky (Russian -skii) in many surnames.

-ic in Medicine

-ic suff.

  1. Of, relating to, or characterized by: carbonic.

  2. Having a valence higher than that of a specified element in compounds or ions named with adjectives ending in -ous: ferric.

  3. Of or relating to an acid: sulfuric acid.