quintuple vs quintuplet

quintuple and quintuplet both are nouns.

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

As nouns, quintuple and quintuplet are synonyms defined as:

quintuple and quintuplet: a set of five similar things considered as a unit

Other synonyms of quintuple include quintet, quintette.

quintuple (noun)	quintuplet (noun)
a set of five similar things considered as a unit	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

quintuple (adjective)	quintuplet (adjective)
having five units or components

quintuple (verb)	quintuplet (verb)
increase fivefold