Kneecap n. : The kneepan.

Kneecap n. : A cap or protection for the knee.

Example:
What do you call the condition where the Kneecap is slipping to the sides?

Taxonomy
bipartite patella, free encyclopedia, knee-joint, Bone, knee, knee cap, femoral condyles, Lateral aspect, triangular bone, femur, the human body, vastus medialis, lower extremity, search, tendon, contracts, muscle, borders.

Defination from the web:
Kneecap) Jump to: navigation, search. For other uses, see Patella ... The patella, also known as the knee cap or kneepan, is a thick, circular-triangular bone which articulates with the femur and covers and protects ...