-ous
-ous , suffix
[Old French -ous, us, -os, French -eux, from Latin -osus, and -us. Compare -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.
(Chemistry) 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.