from
The Collaborative International Dictionary of English v.0.48
-ous \-ous\suff. [OF. -ous, us, -os, F. -eux, fr. L. -osus, and
-us. Cf. {-ose}.]
1. An adjective suffix meaning full of, abounding in, having,
possessing the qualities of, like; as in gracious,
abounding in grace; arduous, full of ardor; bulbous,
having bulbs, bulblike; riotous, poisonous, piteous,
joyous, etc.
[1913 Webster]
2. (Chem.) A suffix denoting that the element indicated by
the name bearing it, has a valence lower than that denoted
by the termination {-ic}; as, nitrous, mercurous, ferrous,
sulphurous, etc., as contrasted with nitric, mercuric,
ferric, sulphuric, etc.
[1913 Webster]