-ous

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; -ph-r-, -phorous; -pter, -pterous; -vore, -vorous.
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).
-ous
suffix
having, full of, or characterized by dangerous, sp-cious, languorous
(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
-ous
suffix forming adjectives from nouns, meaning “having, full of, having to do with, doing, inclined to,” from o.fr. -ous, -eux, from l. -osus.

-ous suff.

possessing; full of; characterized by: filamentous.

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