Source : Webster's Revised Unabridged Dictionary (1913)

Erstwhile \Erst`while"\ (-hw[imac]l"), adv.
   Till then or now; heretofore; formerly. [Archaic]

Source : WordNet®

erstwhile
     adj : belonging to some prior time; "erstwhile friend"; "our
           former glory"; "the once capital of the state"; "her
           quondam lover" [syn: {erstwhile(a)}, {former(a)}, {once(a)},
            {onetime(a)}, {quondam(a)}, {sometime(a)}]
     adv : at a previous time; "once he loved her"; "her erstwhile
           writing" [syn: {once}, {formerly}, {at one time}, {erst}]