Merriam-Webster's Collegiate® Dictionary, 11th Edition
MUSCLE
I. noun
Usage: often attributive see: mouse
Date: 14th century
1. a body tissue consisting of long cells that contract when stimulated and produce motion, an organ that is essentially a mass of muscle tissue attached at either end to a fixed point and that by contracting moves or checks the movement of a body part,
2. muscular strength ; brawn , effective strength ; power ,
II. verb (muscled; muscling)
Date: 1913
transitive verb to move or force by or as if by muscular effort , intransitive verb to make one's way by brute strength or by force