The Collaborative International Dictionary of English v.0.48:

Tibia \Tib"i*a\, n.; pl. Tibiae. [L.]
   1. (Anat.) The inner, or preaxial, and usually the larger, of
      the two bones of the leg or hind limb below the knee.
      [1913 Webster]

   2. (Zool.) The fourth joint of the leg of an insect. See
      Illust. under Coleoptera, and under Hexapoda.
      [1913 Webster]

   3. (Antiq.) A musical instrument of the flute kind,
      originally made of the leg bone of an animal.
      [1913 Webster]

WordNet (r) 3.0 (2006):

tibia
    n 1: the inner and thicker of the two bones of the human leg
         between the knee and ankle [syn: tibia, shinbone, shin
         bone, shin]