c. 1300, name of a game at dice, from Old French hasard, hasart "game of chance played with dice," also "a throw of six in dice" (12c.), of uncertain origin. Possibly from Spanish azar "an unfortunate card or throw at dice," which is said to be from Arabic az-zahr (for al-zahr) "the die." But this is doubtful because of the absence of zahr in classical Arabic dictionaries. Klein suggests Arabic yasara "he played at dice;" Arabic -s- regularly becomes Spanish -z-. The -d was added in French through confusion with the native suffix -ard. Sense evolved in French to "chances in gambling," then "chances in life." In English, sense of "chance of loss or harm, risk" first recorded 1540s.
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."