onstage vs offstage

onstage is not a noun while offstage is a noun.

Word	Noun	Adjective	Verb	Adverb
onstage	No	Yes	No	Yes
offstage	Yes	Yes	No	Yes

onstage (noun)	offstage (noun)
	a stage area out of sight of the audience

onstage (adjective)	offstage (adjective)
situated or taking place on the area of a stage visible to the audience	situated or taking place in the area of a stage not visible to the audience
	concealed from public view or attention

onstage (adverb)	offstage (adverb)
on the stage	behind the scenes; not on stage
	not in public