"a stone-fruit," one with a fleshy or soft outer part and a hard nut or stone at the center (as a plum, cherry, apricot, or peach), 1753, from Modern Latin drupa "stone-fruit," from Latin drupa (oliva) "wrinkled olive," from Greek dryppa, short for drypepes "tree-ripened," from drys "tree" (from PIE root *deru- "be firm, solid, steadfast," with specialized senses "wood, tree") + pepon "ripe" (from PIE root *pekw- "to cook, ripen").
word-forming element denoting "belonging to, of the nature of," from Latin -aceus, enlarged form of adjectival suffix -ax (genitive -acis); see -acea. Especially in biology, "pertaining to X order of plants or animals."
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Harper, D. (n.d.). Etymology of drupaceous. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/drupaceous