A contractile organ consisting of a special bundle of muscle tissue, which moves a particular bone, part, or substance of the body: the heart muscle; the muscles of the arm. A tissue composed of fibers capable of contracting to effect bodily movement. Muscular strength: enough muscle to be a high jumper. Informal Power or authority: put some muscle into law enforcement. To make one's way by or as if by force: muscled into the conversation. To move or force with strength: muscled legislation through Congress.