plant of the group of the pulse family, pea, 1670s, from French légume (16c.), from Latin legumen "pulse, leguminous plant," of unknown origin. One suggestion ties it to Latin legere "to gather" (see lecture (n.)), because they can be scooped by the handful. Middle English had the word in the Latin form legumen (late 14c.).
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."
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Harper, D. (n.d.). Etymology of leguminous. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/leguminous