NICU vs neonatal intensive care unit

NICU and neonatal intensive care unit both are nouns.

Word	Noun	Adjective	Verb	Adverb
NICU	Yes	No	No	No
neonatal intensive care unit	Yes	No	No	No

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

NICU and neonatal intensive care unit: an intensive care unit designed with special equipment to care for premature or seriously ill newborn

NICU (noun)	neonatal intensive care unit (noun)
an intensive care unit designed with special equipment to care for premature or seriously ill newborn	an intensive care unit designed with special equipment to care for premature or seriously ill newborn