c. 1300, "practice of lending money at interest," later, at excessive rates of interest, from Medieval Latin usuria, alteration of Latin usura "payment for the use of money, interest," literally "a usage, use, enjoyment," from usus, from stem of uti (see use (v.)). From mid-15c. as "premium paid for the use of money, interest," especially "exorbitant interest."
word-forming element making adjectives from nouns, meaning "having, full of, having to do with, doing, inclined to," from Old French -ous, -eux, from Latin -osus (compare -ose (1)). In chemistry, "having a lower valence than forms expressed in -ic."