\-ous\ [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.

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, sulphurous, etc., as
   contrasted with nitric, sulphuric, etc.