From The Collaborative International Dictionary of English v.0.48 :
crawdad \craw"dad\ (kr[add]"d[a^]d), crawdaddy
\craw"dad*dy\(kr[add]"d[a^]d*d[y^]), n. (Zool.)
same as crawfish
[PJC] Crawfish
From WordNet (r) 3.0 (2006) :
crawdaddy
n 1: small freshwater decapod crustacean that resembles a
lobster [syn: crayfish, crawfish, crawdad,
crawdaddy]