ICU vs unit

ICU and unit both are nouns.

Word	Noun	Adjective	Verb	Adverb
ICU	Yes	No	No	No
unit	Yes	No	No	No

As nouns, unit is a hypernym of ICU; that is, unit is a word with a broader meaning than ICU:

Other hypernyms of ICU include social unit.

ICU (noun)	unit (noun)
a hospital unit staffed and equipped to provide intensive care	an assemblage of parts that is regarded as a single entity
	a single undivided whole
	an organization regarded as part of a larger social group
	a single undivided natural thing occurring in the composition of something else
	any division of quantity accepted as a standard of measurement or exchange
	an individual or group or structure or other entity regarded as a structural or functional constituent of a whole