WordNet sense 1 (warm-water lobsters without claws; those from Australia and South Africa usually marketed as frozen tails; caught also in Florida and California):

langouste, spiny lobster, rock lobster

WordNet sense 2 (tiny lobster-like crustaceans usually boiled briefly):

crawdad, crawfish, ecrevisse

WordNet sense 3 (small freshwater decapod crustacean that resembles a lobster):

crawdaddy

WordNet sense 4 (large edible marine crustacean having a spiny carapace but lacking the large pincers of true lobsters):

sea crawfish