The Collaborative International Dictionary of English v.0.48:

Bedevil \Be*dev"il\, v. t. [imp. & p. p. Bedevilled (?); p.
   pr. & vb. n. Bedeviling or Bedevilling.]
   1. To throw into utter disorder and confusion, as if by the
      agency of evil spirits; to bring under diabolical
      influence; to torment.
      [1913 Webster]

            Bedeviled and used worse than St. Bartholomew.
                                                  --Sterne.
      [1913 Webster]

   2. To spoil; to corrupt. --Wright.
      [1913 Webster]

WordNet (r) 3.0 (2006):

bedevil
    v 1: treat cruelly; "The children tormented the stuttering
         teacher" [syn: torment, rag, bedevil, crucify,
         dun, frustrate]
    2: be confusing or perplexing to; cause to be unable to think
       clearly; "These questions confuse even the experts"; "This
       question completely threw me"; "This question befuddled even
       the teacher" [syn: confuse, throw, fox, befuddle,
       fuddle, bedevil, confound, discombobulate]

Moby Thesaurus II by Grady Ward, 1.0:

67 Moby Thesaurus words for "bedevil":
   aggravate, annoy, badger, bait, be at, beset, bewitch, bother,
   bristle, brown off, bug, bullyrag, burn up, chivy, demonize, devil,
   devilize, diabolize, discompose, distemper, disturb, dog,
   exasperate, exercise, fash, get, gripe, harass, harry, heckle,
   hector, hex, hoodoo, hound, irk, jinx, miff, molest, nag, needle,
   nettle, nudzh, obsess, overlook, peeve, persecute, pester, pick on,
   pique, plague, pluck the beard, possess, pother, provoke, ride,
   rile, roil, ruffle, tantalize, tease, torment, try the patience,
   tweak the nose, vex, voodoo, witch, worry