littermate
/ˈlɪtərˌmeɪt/
noun
- One of a group of young animals born to the same mother at the same time.
- The two puppies were littermates and had been inseparable since birth.
- We adopted one kitten from the shelter and later found its littermate.
- The breeder kept one of the pups and sold the rest of the littermates.
Synonyms