sibling vs quintuplet

sibling and quintuplet both are nouns.

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

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

sibling: a person's brother or sister
quintuplet: one of five children born at the same time from the same pregnancy

Other hyponyms of sibling include half blood, quad, quadruplet, quin, quint, triplet, twin.

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