islet vs island

islet and island both are nouns.

Word	Noun	Adjective	Verb	Adverb
islet	Yes	No	No	No
island	Yes	No	No	No

As nouns, island is a hypernym of islet; that is, island is a word with a broader meaning than islet:

islet (noun)	island (noun)
a small island	a zone or area resembling an island
	a land mass (smaller than a continent) that is surrounded by water