Source : Webster's Revised Unabridged Dictionary (1913)

Withdrawer \With*draw"er\, n.
   One who withdraws; one who takes back, or retracts.

Source : WordNet®

withdrawer
     n 1: an authority who withdraws permission
     2: an individualist who withdraws from social interaction
     3: a drug addict who is discontinuing the use of narcotics
     4: a contestant who withdraws from competition
     5: a student who withdraws from the educational institution in
        which he or she was enrolled
     6: a depositor who withdraws funds previously deposited