erstwhile vs sometime

erstwhile and sometime both are adjectives.

Word	Noun	Adjective	Verb	Adverb
erstwhile	No	Yes	No	Yes
sometime	No	Yes	No	Yes

As adjectives, erstwhile and sometime are synonyms defined as:

Other synonyms of erstwhile include former, old, one-time, onetime, quondam.

erstwhile (adjective)	sometime (adjective)
belonging to some prior time	belonging to some prior time

erstwhile (adverb)	sometime (adverb)
at a previous time	at some indefinite or unstated time