The Collaborative International Dictionary of English v.0.48:

Pitfall \Pit"fall`\, n.
   A pit deceitfully covered to entrap wild beasts or men; a
   trap of any kind. --Sir T. North.
   [1913 Webster]

WordNet (r) 3.0 (2006):

pitfall
    n 1: an unforeseen or unexpected or surprising difficulty [syn:
         pitfall, booby trap]
    2: a trap in the form of a concealed hole [syn: pit,
       pitfall]