tripper in WordNet English dictionary

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