The Collaborative International Dictionary of English v.0.48:

Bourdon \Bour"don\, n. [F., fr. L. burdo mule, esp. one used for
   carrying litters. Cf. Sp. muleta a young she mule; also,
   crutch, prop.]
   A pilgrim's staff.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Bourdon \Bour"don`\, n. [F. See Burden a refrain.] (Mus.)
   (a) A drone bass, as in a bagpipe, or a hurdy-gurdy. See
       Burden (of a song.)
   (b) A kind of organ stop.
       [1913 Webster]

WordNet (r) 3.0 (2006):

bourdon
    n 1: a pipe of the bagpipe that is tuned to produce a single
         continuous tone [syn: drone, drone pipe, bourdon]