Muscle  —n. 1 fibrous tissue producing movement in or maintaining the position of an animal body. 2 part of an animal body that is composed of muscles. 3 strength, power. —v. (-ling) (foll. By in, in on) colloq. Force oneself on others; intrude by forceful means.  not move a muscle be completely motionless. [latin diminutive of mus mouse]