Answer: littermate

AnswerCrossword Clue
LITTERMATEPup, to a sibling, e.g.
LITTERMATEAny in a group of puppies
LITTERMATEOne puppy to another
LITTERMATEAlmost every puppy has one
LITTERMATEThe one puppy that can read?
littermateOne member of a pair or group of animals born in the same litter
littermateone who shares the same litter