erstwhile
adjective·/ˈɝːst.waɪl/
Former, belonging to an earlier time, especially a role, status, or association that has since ended. The word often carries a faint narrative quality, suggesting what someone used to be.
Her erstwhile rival sat beside her now, and the old competition felt like a story they’d both outgrown.
adverb
In former times; once (archaic; literary).
Erstwhile, the street had been all small shops; now it was glass and silence.
Etymology
From Middle English erst whil(e) “at first, earlier,” from erst “formerly” + while “time.” The word is time made compact: a formerness you can say in one breath.
Related Words
formerthe plain modern equivalent
quondamanother learned “former,” more antique in tone
bygonepast with a wistful emphasis
ex-prefix form: ex-partner, ex-president; more abrupt