ICU vs intensive care unit

ICU and intensive care unit both are nouns.

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

As nouns, ICU and intensive care unit are synonyms defined as:

ICU and intensive care unit: a hospital unit staffed and equipped to provide intensive care

ICU (noun)	intensive care unit (noun)
a hospital unit staffed and equipped to provide intensive care	a hospital unit staffed and equipped to provide intensive care