portmanteau word vs neologism

portmanteau word and neologism both are nouns.

Word	Noun	Adjective	Verb	Adverb
portmanteau word	Yes	No	No	No
neologism	Yes	No	No	No

As nouns, neologism is a hypernym of portmanteau word; that is, neologism is a word with a broader meaning than portmanteau word:

portmanteau word: a new word formed by joining two others and combining their meanings
neologism: a newly invented word or phrase

Other hypernyms of portmanteau word include coinage, neology.

portmanteau word (noun)	neologism (noun)
a new word formed by joining two others and combining their meanings	the act of inventing a word or phrase
	a newly invented word or phrase