Two nonidentical twins: rump and runt?
Rump and runt are not twins, but they sound somewhat alike, and they may be “distantly related,” to use a phrase sometimes occurring in dictionaries, though this phrase is too vague to be useful. Rump surfaced in texts only in the fifteenth century, and but for the Rump Parliament (1648-1653), famous in British History, the word would probably have been relegated mainly to talks about animals and bird.