See

1. Small freshwater decapod crustacean that resembles a lobster; SYN. crawfish, crawdad, crawdaddy.
2. Tiny lobster-like crustaceans usually boiled briefly; SYN. crawfish, crawdad, ecrevisse.
Freshwater decapod (ten-limbed) crustacean belonging to several families structurally similar to, but smaller than, the lobster. Crayfish are brownish-green scavengers and are found in all parts of the world except Africa. They are edible, and some species are farmed.
The spiny lobster Palinurus vulgaris, is sometimes called crayfish; it is actually a marine lobster without pincers, and grows up to 50 cm/20 in long.

ETYM AS. loppestre, lopystre prob., corrupted from Latin locusta a marine shellfish, a kind of lobster, a locust. Related to Locust.
1. Any of several edible marine crustaceans of the families Homaridae and Nephropsidae and Palinuridae.
2. Flesh of a lobster.
Large marine crustacean of the order Decapoda. Lobsters are grouped with freshwater crayfish in the suborder Reptantia (“walking”), although both lobsters and crayfish can also swim, using their fanlike tails. Lobsters have eyes on stalks and long antennae, and are mainly nocturnal. They scavenge and eat dead or dying fish.
True lobsters, family Homaridae, are distinguished by having very large “claws” or pincers on their first pair of legs, and smaller ones on their second and third pairs. Spiny lobsters, family Palinuridae, have no large pincers. They communicate by means of a serrated pad at the base of their antennae, the “sound” being picked up by sensory nerves located on hairlike outgrowths on their fellow lobsters up to 60 m/180 ft away.
Species include the American lobster Homarus americanus; and the Norwegian lobster Nephrops norvegicus, a small orange species.