coronary care unit vs ICU

coronary care unit and ICU both are nouns.

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

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

coronary care unit: a hospital unit specially staffed and equipped to treat patients with serious cardiac problems
ICU: a hospital unit staffed and equipped to provide intensive care

Other hypernyms of coronary care unit include intensive care unit.

coronary care unit (noun)	ICU (noun)
a hospital unit specially staffed and equipped to treat patients with serious cardiac problems	a hospital unit staffed and equipped to provide intensive care