udder (n.) Look up udder at Dictionary.com
Old English udder "milk gland of a cow, goat, etc.," from Proto-Germanic *udr- (cf. Old Frisian and Middle Dutch uder, Old High German utar, German Euter, and, with unexplained change of consonant, Old Norse jugr), from PIE *udhr- (cf. Sanskrit udhar, Greek outhar, Latin uber "udder").