portico vs narthex

portico and narthex both are nouns.

Word	Noun	Adjective	Verb	Adverb
portico	Yes	No	No	No
narthex	Yes	No	No	No

As nouns, narthex is a hyponym of portico; that is, narthex is a word with a more specific, narrower meaning than portico:

portico: a porch or entrance to a building consisting of a covered and often columned area
narthex: portico at the west end of an early Christian basilica or church

portico (noun)	narthex (noun)
a porch or entrance to a building consisting of a covered and often columned area	a vestibule leading to the nave of a church
	portico at the west end of an early Christian basilica or church