preterm infant vs preemie

preterm infant and preemie both are nouns.

Word	Noun	Adjective	Verb	Adverb
preterm infant	Yes	No	No	No
preemie	Yes	No	No	No

As nouns, preterm infant and preemie are synonyms defined as:

preterm infant and preemie: an infant that is born prior to 37 weeks of gestation

Other synonyms of preterm infant include premature baby, premature infant, premie, preterm baby.

preterm infant (noun)	preemie (noun)
an infant that is born prior to 37 weeks of gestation	an infant that is born prior to 37 weeks of gestation