femur

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A bone of the leg situated between the pelvis and knee in humans. It is the largest and strongest bone in the body.
• noun A functionally similar bone in the leg or hind limb of other vertebrates.
• noun The thick, most muscular segment of the insect leg, situated between the trochanter and the tibia.

from The Century Dictionary.

• noun The thigh.
• noun In anatomy, the thigh-bone; the single long bone which extends along the thigh from the hip-joint to the knee-joint, articulating above with the pelvis, and below with the tibia, or the tibia and fibula.
• noun In entomology, the thigh; the third joint of the leg, between the trochanter and the shank or tibia. See cut under corbiculum.
• noun In architecture, the interstitial member between two channels in the triglyph of the Doric order.

from the GNU version of the Collaborative International Dictionary of English.

• noun The thigh bone; -- it is the longest and thickest bone of the human skeleton, which extends from the pelvis to the knee.
• noun The proximal segment of the hind limb containing the thigh bone; the thigh. See coxa.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun anatomy A thighbone.
• noun A segment of the leg of an insect or arachnid.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the longest and thickest bone of the human skeleton; extends from the pelvis to the knee