Wiktionary
oyster mushroom
n. 1 (context US English) The mushroom ''Pleurotus ostreatus'', which in the wild grows chiefly on hardwood trees, and is cultivated for food. 2 Any of several mushrooms of the genus ''Pleurotus'' cultivated for food.
WordNet
oyster mushroom
n. edible agaric with a soft grayish cap growing in shelving masses on dead wood [syn: oyster fungus, oyster agaric, Pleurotus ostreatus]