Definition of oyster
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 oyster
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
