The Collaborative International Dictionary of English v.0.48:

Kneepan \Knee"pan`\, n. (Anat.)
   A roundish, flattened, sesamoid bone in the tendon in front
   of the knee joint; the patella; the kneecap.
   [1913 Webster]

WordNet (r) 3.0 (2006):

kneepan
    n 1: a small flat triangular bone in front of the knee that
         protects the knee joint [syn: patella, kneecap,
         kneepan]