oyster

Concise Oxford English Dictionary © 2008 Oxford University Press:
oyster/ˈɔɪstə(r)/

▶noun

• 1 a bivalve marine mollusc with a rough, flattened, irregularly oval shell, several kinds of which are farmed for food or pearls. [Ostrea edulis (Europe), Crassostrea virginica (America), and other species.]

• 2 a shade of greyish white.

• 3 an oval morsel of meat on each side of the backbone in poultry.

– phrases
the world is one's oyster one is in a position to enjoy a broad range of opportunities. [from Shakespeare's Merry Wives of Windsor (ii. ii. 5).]

– origin ME: from OFr. oistre, via L. from Gk ostreon; rel. to osteon ‘bone’ and ostrakon ‘shell or tile’.