Webster's Revised Unabridged Dictionary · 1913

Crawfish

Crawfish (kra"fish`) , noun

[Corrupted from Old English crevis, creves, Old French crevice, French écrevisse, from Old High German krebiz crab, German krebs. See Crab. The ending -fish arose from confusion with English fish.]

(Zoology) Any decapod crustacean of the family Astacida (genera Cambarus and Cambarus), resembling the lobster, but smaller, and found in fresh waters. Crawfishes are esteemed very delicate food both in Europe and America. The North American species are numerous and mostly belong to the genus Cambarus. The blind crawfish of the Mammoth Cave is Cambarus pellucidus. The common European species is Astacus fluviatilis.
2.
tiny lobsterlike crustaceans usually boiled briefly.
3.
a large edible marine crustacean having a spiny carapace but lacking the large pincers of true lobsters.

Also: Crayfish

crawfish , intransitive verb

to back out in a humiliating manner; as, We'll have to crawfish out from meeting with him.