triplet vs sibling

triplet and sibling both are nouns.

Word	Noun	Adjective	Verb	Adverb
triplet	Yes	No	No	No
sibling	Yes	No	No	No

As nouns, sibling is a hypernym of triplet; that is, sibling is a word with a broader meaning than triplet:

triplet: one of three offspring born at the same time from the same pregnancy
sibling: a person's brother or sister

Other hypernyms of triplet include sib.

triplet (noun)	sibling (noun)
a set of three similar things considered as a unit	a person's brother or sister
one of three offspring born at the same time from the same pregnancy
the cardinal number that is the sum of one and one and one