narthex vs antechamber

narthex and antechamber both are nouns.

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

As nouns, antechamber is a hypernym of narthex; that is, antechamber is a word with a broader meaning than narthex:

Other hypernyms of narthex include anteroom, entrance hall, foyer, hall, lobby, vestibule.

narthex (noun)	antechamber (noun)
a vestibule leading to the nave of a church	a large entrance or reception room or area
portico at the west end of an early Christian basilica or church