hypo-

1.
a prefix appearing in loanwords from Greek, where it meant “under” (hypostasis); on this model used, especially as opposed to hyper-, in the formation of compound words (hypothyroid).
Also, especially before a vowel, hyp-.
Origin
< Greek, combining form of hypó under (preposition), below (adv.); cognate with Latin sub (see sub-); cf. up
Can be confused
hyper-, hypo-.
British Dictionary definitions for hypo-

hypo-

prefix
1.
under, beneath, or below: hypodermic
2.
lower; at a lower point: hypogastrium
3.
less than: hypoploid
4.
(in medicine) denoting a deficiency or an abnormally low level: hypothyroid, hypoglycaemia
5.
incomplete or partial: hypoplasia
6.
indicating that a chemical compound contains an element in a lower oxidation state than usual: hypochlorous acid
Word Origin
from Greek, from hupo under

Hypo-

prefix
1.
indicating a plagal mode in music: Hypodorian
Word Origin
from Greek: beneath (it lies a fourth below the corresponding authentic mode)
Word Origin and History for hypo-

word-forming element meaning "under, beneath" (in chemistry, indicating a lesser oxidation), from hypo-, comb. form of Greek hypo (prep. and adverb) "under," from PIE *upo- "under, up from under, over" (see sub-).

hypo- in Medicine

hypo- or hyp-
pref.

  1. Below; beneath; under: hypochondriac.

  2. Less than normal; deficient: hypofunction.

  3. In the lowest state of oxidation: hypoxanthine.

hypo- in Science
hypo- or hyp-  
A prefix that means "beneath" or "below," as in hypodermic, below the skin. It also means "less than normal," especially in medical terms like hypoglycemia. In the names of chemical compounds, it means "at the lowest state of oxidation," as in sodium hypochlorite.