biceps

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

• noun A muscle with two heads or points of origin.
• noun The large muscle at the front of the upper arm that flexes the forearm.
• noun The large muscle at the back of the thigh that flexes the knee joint.

from The Century Dictionary.

• noun In anatomy, a muscle having two heads or origins; specifically, the biceps brachii.
• noun Figuratively, strength or muscular development.
• noun Muscular strength of the arm; ability to use the arm effectively: from such strength or ability depending on the development of the biceps muscle.

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

• noun (Anat.) A muscle having two heads or origins; -- applied particularly to a flexor in the arm, and to another in the thigh.

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

• noun anatomy Any muscle having two heads.
• noun Specifically, the biceps brachii, the flexor of the elbow.
• noun informal The upper arm, especially the collective muscles of the upper arm.
• noun prosody A point in a metrical pattern that can be filled either with one long syllable (a longum) or two short syllables (two brevia)

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

• noun any skeletal muscle having two origins (but especially the muscle that flexes the forearm)