The Collaborative International Dictionary of English v.0.48:

Tripper \Trip"per\, n.
   1. One who trips or supplants; also, one who walks or trips
      nimbly; a dancer.
      [1913 Webster]

   2. An excursionist.
      [1913 Webster]

WordNet (r) 3.0 (2006):

tripper
    n 1: (slang) someone who has taken a psychedelic drug and is
         undergoing hallucinations
    2: a walker or runner who trips and almost falls [syn:
       stumbler, tripper]
    3: a tourist who is visiting sights of interest [syn:
       sightseer, excursionist, tripper, rubberneck]
    4: a catch mechanism that acts as a switch; "the pressure
       activates the tripper and releases the water" [syn:
       tripper, trip]

Moby Thesaurus II by Grady Ward, 1.0:

78 Moby Thesaurus words for "tripper":
   LSD user, acidhead, addict, adventurer, alcoholic, alpinist,
   astronaut, camper, chain smoker, climber, cocaine sniffer, cokie,
   comers and goers, commuter, cosmopolite, cruiser, cubehead,
   dipsomaniac, dope fiend, doper, drug abuser, drug addict,
   drug user, drunkard, excursionist, explorer, fare, fiend, freak,
   globe-girdler, globe-trotter, glue sniffer, goer, habitual, hajji,
   head, heavy smoker, hophead, hype, jet set, jet-setter, journeyer,
   junkie, marijuana smoker, mariner, methhead, mountaineer,
   narcotics addict, palmer, passenger, passerby, pathfinder, pilgrim,
   pillhead, pioneer, pothead, rubberneck, rubbernecker, sailor,
   sightseer, snowbird, speed freak, straphanger, tourer, tourist,
   trailblazer, trailbreaker, transient, traveler, trekker, user,
   viator, visiting fireman, voortrekker, voyager, voyageur, wayfarer,
   world-traveler