The Collaborative International Dictionary of English v.0.48:
Crawfish \Craw"fish`\ (kr[add]"f[i^]sh`), Crayfish \Cray"fish`\
(kr[=a]"f[i^]sh`), n.; pl. -fishes or -fish. [Corrupted
fr. OE. crevis, creves, OF. crevice, F. ['e]crevisse, fr.
OHG. krebiz crab, G. krebs. See Crab. The ending -fish
arose from confusion with E. fish.] (Zool.)
Any decapod crustacean of the family Astacid[ae] (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
Syn: crawdad, crawdaddy.
2. tiny lobsterlike crustaceans usually boiled briefly.
Syn: crawdad, ecrevisse.
3. a large edible marine crustacean having a spiny carapace
but lacking the large pincers of true lobsters.
Syn: spiny lobster, langouste, rock lobster, crayfish, sea