-ous

Where it comes from

From Middle English -ous, from Old French -ous, -os, -us, from Latin -ōsus (“full of”). Doublet of -ose and -wise in unstressed position. Many English adjectives ending in -ous were taken from preexisting French or Latin adjectives that end in one of the above suffixes (e.g. envious corresponds directly to Old French envious which in turn corresponds directly to Latin invidiōsus). In addition, -ous (or the variant form -ious) has at times been attached to English nouns to form derived adjectives that lack precedents in French or Latin, such as slumberous from slumber or blizzardous from blizzard. It has also been used in some cases as a means of adapting adjectives borrowed from Latin that originally ended simply in -us, -a, -um (for example, obvious and previous are derived from Latin obvius and praevius, not *obviōsus or *praeviōsus).