A person's brother or sister. Classified under: Nouns denoting people. Synonyms: sib; sibling. Hypernyms (sibling is a kind of...): relation; relative (a person related by blood or marriage) Hyponyms (each of the following is a kind of sibling): half blood (one of siblings who have only one parent in common) quad; quadruplet (one of four children born at the same time from the same pregnancy) quin; quint; quintuplet (one of five children born at the same time from the same pregnancy)