noun (n)

• (slang) someone who has taken a psychedelic drug and is undergoing hallucinations(noun.person)

  source: wordnet30
• a walker or runner who trips and almost falls(noun.person)

  Synonym:
  stumbler
  

  source: wordnet30
• a tourist who is visiting sights of interest(noun.person)

  Synonym:
  excursionist, rubberneck, sightseer
  

  source: wordnet30
• a catch mechanism that acts as a switch(noun.artifact)

  Example:
  The pressure activates the tripper and releases the water.
  

  Synonym:
  trip
  

  source: wordnet30
• One who trips or supplants; also, one who walks or trips nimbly; a dancer.(noun)

  source: webster1913