WordNet (r) 3.0 (2006):

jump on
    v 1: get up on the back of; "mount a horse" [syn: hop on,
         mount, mount up, get on, jump on, climb on,
         bestride] [ant: get off, hop out]

Moby Thesaurus II by Grady Ward, 1.0:

49 Moby Thesaurus words for "jump on":
   asphyxiate, bottle up, call down, censor, choke off, clamp down on,
   come down on, cork, cork up, crack down on, crush, damp down,
   dress down, drown, extinguish, gag, give it to, hold down,
   jump all over, keep down, keep under, kill, muzzle, pour water on,
   put down, quash, quell, quench, repress, shut down on, silence,
   sit down on, sit on, smash, smother, speak to, squash, squelch,
   stanch, stifle, strangle, stultify, subdue, suffocate, suppress,
   talk to, tell off, throttle, trim