WordNet (r) 3.0 (2006):

mess around
    v 1: do random, unplanned work or activities or spend time idly;
         "The old lady is usually mucking about in her little house"
         [syn: putter, mess around, potter, tinker,
         monkey, monkey around, muck about, muck around]

Moby Thesaurus II by Grady Ward, 1.0:

84 Moby Thesaurus words for "mess around":
   Paul-Pry, bat out, botch, bungle, busybody, butt in, coquet,
   dabble, dally, dash off, do anyhow, do by halves, do carelessly,
   do offhand, doodle, fake up, fiddle, fiddle with, fiddle-faddle,
   fidget with, finger with, flirt, fool, fool around, fool with,
   fribble, frivol, fudge up, horn in, horse around, idle, interfere,
   interlope, intermeddle, jerk off, jury-rig, kibitz, kid around,
   knock off, knock out, knock together, lash up, loiter, meddle,
   meddle with, mess, mess with, monkey, monkey around, monkey with,
   nose, patch, patch together, patch up, piddle, play, play around,
   play with, potter, pound out, pry, puddle, putter, rough out,
   roughcast, roughhew, slap up, smatter, snoop, tamper, tamper with,
   throw off, throw together, tinker, toss off, toss out,
   toss together, toy, toy with, trifle, trifle with, twiddle,
   whomp up, womanize