The Collaborative International Dictionary of English v.0.48:

Supervisor \Su`per*vis"or\, n.
   1. One who supervises; an overseer; an inspector; a
      superintendent; as, a supervisor of schools.
      [1913 Webster]

   2. A spectator; a looker-on. [Obs.] --Shak.
      [1913 Webster]

WordNet (r) 3.0 (2006):

supervisor
    n 1: one who supervises or has charge and direction of
    2: a program that controls the execution of other programs [syn:
       supervisory program, supervisor, executive program]