In full Marennes oyster. An edible oyster, Ostrea edulis, of a variety farmed in the region of Marennes, noted for its grey or green colour and excellent flavour.
Origin
Early 20th century; earliest use found in The New English Dictionary. From French Marennes from Marennes, the name of a coastal town in the department of Charente-Maritime in western France, where the oysters are cultivated.