-ous

1.
a suffix forming adjectives that have the general sense “possessing, full of” a given quality (covetous; glorious; nervous; wondrous); -ous, and its variant -ious, have often been used to Anglicize Latin adjectives with terminations that cannot be directly adapted into English (atrocious; contiguous; garrulous; obvious; stupendous). As an adjective-forming suffix of neutral value, it regularly Anglicizes Greek and Latin adjectives derived without suffix from nouns and verbs; many such formations are productive combining forms in English, sometimes with a corresponding nominal combining form that has no suffix;
Compare -fer, -ferous; -phore, -phorous; -pter, -pterous; -vore, -vorous.
2.
a suffix forming adjectival correspondents to the names of chemical elements; specialized, in opposition to like adjectives ending in -ic, to mean the lower of two possible valences (stannous chloride, SnCl 2 , and stannic chloride SnCl 4).
Origin
Middle English < Anglo-French, Old French < Latin -ōsus; a doublet of -ose1
British Dictionary definitions for -ous

-ous

suffix
1.
having, full of, or characterized by: dangerous, spacious, languorous
2.
(in chemistry) indicating that an element is chemically combined in the lower of two possible valency states: ferrous, stannous Compare -ic (sense 2)
Word Origin
from Old French, from Latin -ōsus or -us, Greek -os, adj suffixes
Word Origin and History for -ous

word-forming element making adjectives from nouns, meaning "having, full of, having to do with, doing, inclined to," from Old French -ous, -eux, from Latin -osus (cf. -ose (1)). In chemistry, "having a lower valence than forms expressed in -ic."

-ous in Medicine

-ous suff.

  1. Possessing; full of; characterized by: filamentous.

  2. Having a valence lower than that of a specified element in compounds or ions named with adjectives ending in -ic: ferrous.