[oys.ter] n, often attrib [ME oistre, fr. MF, fr. L ostrea, fr. Gk ostreon; akin to Gk ostrakon shell, osteon bone--more at osseous] (13c) 1 a: any of various marine bivalve mollusks (family Ostreidae) that have a rough irregular shell closed by a single adductor muscle and include commercially important shellfish b: any of various mollusks resembling or related to the oysters
2: something that is or can be readily made to serve one's personal ends "the world was her ~"
3: a small mass of muscle contained in a concavity of the pelvic bone on each side of the back of a fowl
4: an extremely taciturn person
5: a grayish-white color