newborn vs infant

newborn and infant both are nouns.

Word	Noun	Adjective	Verb	Adverb
newborn	Yes	Yes	No	No
infant	Yes	No	No	No

As nouns, infant is a hypernym of newborn; that is, infant is a word with a broader meaning than newborn:

newborn: a baby from birth to four weeks
infant: a very young child (birth to 1 year) who has not yet begun to walk or talk

Other hypernyms of newborn include babe, baby.

newborn (noun)	infant (noun)
a baby from birth to four weeks	a very young child (birth to 1 year) who has not yet begun to walk or talk

newborn (adjective)	infant (adjective)
having just or recently arisen or come into existence
recently born