The Collaborative International Dictionary of English v.0.48:

Knee \Knee\ (n[=e]), n. [OE. kne, cneo, As. cne['o], cne['o]w;
   akin to OS. knio, kneo, OFries. kn[imac], G. & D. knie, OHG.
   chniu, chneo, Icel. kn[=e], Sw. kn[aum], Dan. kn[ae], Goth.
   kniu, L. genu, Gr. go`ny, Skr. j[=a]nu, [root]231. Cf.
   Genuflection.]
   1. In man, the joint in the middle part of the leg.
      [1913 Webster]

   2. (Anat.)
      (a) The joint, or region of the joint, between the thigh
          and leg.
      (b) In the horse and allied animals, the carpal joint,
          corresponding to the wrist in man.
          [1913 Webster]

   3. (Mech. & Shipbuilding) A piece of timber or metal formed
      with an angle somewhat in the shape of the human knee when
      bent.
      [1913 Webster]

   4. A bending of the knee, as in respect or courtesy.
      [1913 Webster]

            Give them title, knee, and approbation. --Shak.
      [1913 Webster]

   Knee breeches. See under Breeches.

   Knee holly, Knee holm (Bot.), butcher's broom.

   Knee joint. See in the Vocabulary.

   Knee timber, timber with knees or angles in it.

   Knee tribute, or Knee worship, tribute paid by kneeling;
      worship by genuflection. [Obs.] "Knee tribute yet unpaid."
      --Milton.
      [1913 Webster]

WordNet (r) 3.0 (2006):

knee joint
    n 1: hinge joint in the human leg connecting the tibia and
         fibula with the femur and protected in front by the patella
         [syn: knee, knee joint, human knee, articulatio
         genus, genu]