apse vs apsis

apse and apsis both are nouns.

Word	Noun	Adjective	Verb	Adverb
apse	Yes	No	No	No
apsis	Yes	No	No	No

As nouns, apse and apsis are synonyms defined as:

apse and apsis: a domed or vaulted recess or projection on a building especially the east end of a church; usually contains the altar

apse (noun)	apsis (noun)
a domed or vaulted recess or projection on a building especially the east end of a church; usually contains the altar	a domed or vaulted recess or projection on a building especially the east end of a church; usually contains the altar