Adjective has 1 sense

• erstwhile(s = adj.all) former, old, one-time, onetime, quondam, sometime - belonging to some prior time; "erstwhile friend"; "her quondam lover"; "our former glory"; "the once capital of the state"

Adverbial has 1 sense

• erstwhile(r = adv.all) at one time, erst, formerly, once - at a previous time; "at one time he loved her"; "her erstwhile writing"; "she was a dancer once"