Muscle
late Middle English: from French, from Latin musculus, diminutive of mus ‘mouse’ (some muscles being thought to be mouse-like in form).
wiktionary
From Middle English muscle, muscule, muskylle, and in part from Middle French muscle, from Latin mūsculus(“a muscle”, literally “little mouse”) because of the mouselike appearance of some muscles, from mūs(“mouse”). Doublet of mussel. More at mouse.
etymonline
muscle (n.)
"contractible animal tissue consisting of bundles of fibers," late 14c., "a muscle of the body," from Latin musculus "a muscle," literally "a little mouse," diminutive of mus "mouse" (see mouse (n.)).
So called because the shape and movement of some muscles (notably biceps) were thought to resemble mice. The analogy was made in Greek, too, where mys is both "mouse" and "muscle," and its combining form gives the medical prefix myo-. Compare also Old Church Slavonic mysi "mouse," mysica "arm;" German Maus "mouse; muscle," Arabic 'adalah "muscle," 'adal "field mouse;" Cornish logodenfer "calf of the leg," literally "mouse of the leg." In Middle English, lacerte, from the Latin word for "lizard," also was used as a word for a muscle.
Musclez & lacertez bene one selfe þing, Bot þe muscle is said to þe fourme of mouse & lacert to þe fourme of a lizard. [Guy de Chauliac, "Grande Chirurgie," c. 1425]
Hence muscular and mousy are relatives, and a Middle English word for "muscular" was lacertous, "lizardy." Figurative sense of "muscle, strength, brawn" is by 1850; that of "force, violence, threat of violence" is 1930, American English. Muscle car "hot rod" is from 1969.
muscle (v.)
1913, "to accomplish by strength," from muscle (n.). Meaning "coerce by violence or pressure" is by 1929 in U.S. underworld slang. Related: Muscled; muscling.
