traffic island vs island

traffic island and island both are nouns.

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

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

traffic island: a curbed area in a roadway from which traffic is excluded; provides safe area for pedestrians
island: a zone or area resembling an island

traffic island (noun)	island (noun)
a curbed area in a roadway from which traffic is excluded; provides safe area for pedestrians	a zone or area resembling an island
	a land mass (smaller than a continent) that is surrounded by water