-acious

word-forming element in Modern Latin making names for orders and classes in zoology (Crustacea, Cetacea, etc.), from Latin -acea, neuter plural of -aceus "belonging to, of the nature of" (enlarged from adjectival suffix -ax, genitive -acis).

The names are thus formally adjectives, Latin animalia "animals" (a neuter plural noun) being understood. Thus Crustacea "shellfish" are *crustacea animalia "crusty animals."

In botany, the suffix is -aceae, from the fem. plural of -aceus, forming orders or families of plants (Rosaceae, etc.) with a presumed plantae "plants," which is a fem. plural.

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."

also predaceous, "living by prey, disposed to prey or plunder, predatory," 1713, from stem of predation (Latin praedari) + -acious.