The Collaborative International Dictionary of English v.0.48:

invigilate \invigilate\ n. ([i^]n*v[i^]j"[i^]l*[=a]t) [imp. & p.
   p. Invigilated ([i^]n*v[i^]j"[i^]l*[=a]`t[e^]d); p. pr. &
   vb. n. Invigilating.] [L. invigilare to stay awake, to be
   vigilant.]
   To keep watch.
   [PJC]

   2. To keep watch over examination candidates to prevent
      cheating. [British]
      [WordNet 1.5]

WordNet (r) 3.0 (2006):

invigilate
    v 1: watch over (students taking an exam, to prevent cheating)
         [syn: invigilate, proctor]