sib vs triplet

sib and triplet both are nouns.

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

As nouns, triplet is a hyponym of sib; that is, triplet is a word with a more specific, narrower meaning than sib:

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

Other hyponyms of sib include half blood, quad, quadruplet, quin, quint, quintuplet, twin.

sib (noun)	triplet (noun)
one related by blood or origin; especially on sharing an ancestor with another	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