quintuplet vs sibling

quintuplet and sibling both are nouns.

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

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

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

Other hypernyms of quintuplet include sib.

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