The Collaborative International Dictionary of English v.0.48:

Rappel \Rap"pel\ (r[a^]p"p[e^]l or r[a^]p*p[e^]l"), n. [F. Cf.
   Repeal.] (Mil.)
   The beat of the drum to call soldiers to arms.
   [1913 Webster]

WordNet (r) 3.0 (2006):

rappel
    n 1: (mountaineering) a descent of a vertical cliff or wall made
         by using a doubled rope that is fixed to a higher point and
         wrapped around the body [syn: rappel, abseil]
    v 1: lower oneself with a rope coiled around the body from a
         mountainside; "The ascent was easy--roping down the
         mountain would be much more difficult and dangerous"; "You
         have to learn how to abseil when you want to do technical
         climbing" [syn: rappel, abseil, rope down]