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[muhs-uh l] /ˈmʌs əl/
a tissue composed of cells or fibers, the contraction of which produces movement in the body.
an organ, composed of muscle tissue, that contracts to produce a particular movement.
muscular strength; brawn:
It will take a great deal of muscle to move this box.
power or force, especially of a coercive nature:
They put muscle into their policy and sent the marines.
lean meat.
  1. a hired thug or thugs.
  2. a bodyguard or bodyguards:
    a gangster protected by muscle.
a necessary or fundamental thing, quality, etc.:
The editor cut the muscle from the article.
verb (used with object), muscled, muscling.
Informal. to force or compel others to make way for:
He muscled his way into the conversation.
to make more muscular:
The dancing lessons muscled her legs.
to strengthen or toughen; put muscle into.
Informal. to accomplish by muscular force:
to muscle the partition into place.
Informal. to force or compel, as by threats, promises, influence, or the like:
to muscle a bill through Congress.
verb (used without object), muscled, muscling.
Informal. to make one's way by force or fraud (often followed by in or into).
Informal. (of a machine, engine, or vehicle) being very powerful or capable of high-speed performance:
a muscle power saw.
Origin of muscle
1525-35; < Latin mūsculus literally, little mouse (from fancied resemblance to some muscles), equivalent to mūs mouse + -culus -cle1
Related forms
muscleless, adjective
muscly, adjective
overmuscled, adjective
transmuscle, noun
unmuscled, adjective
3. power, vigor, might, force. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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British Dictionary definitions for muscle in


a tissue composed of bundles of elongated cells capable of contraction and relaxation to produce movement in an organ or part
an organ composed of muscle tissue
strength or force
(intransitive; often foll by in, on, etc) (informal) to force one's way (in)
Derived Forms
muscly, adjective
Word Origin
C16: from medical Latin musculus little mouse, from the imagined resemblance of some muscles to mice, from Latin mūs mouse
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for muscle in



late 14c., from Middle French muscle "muscle, sinew" (14c.) and directly from Latin musculus "a muscle," literally "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 comb. form gives the medical prefix myo-. Cf. also Old Church Slavonic mysi "mouse," mysica "arm;" German Maus "mouse; muscle," Arabic 'adalah "muscle," 'adal "field mouse." 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 "force, violence, threat of violence" is 1930, American English. Muscle car "hot rod" is from 1969.



1913, "to accomplish by strength," from muscle (n.). Related: Muscled; muscling. To muscle in is 1929 in underworld slang.

Online Etymology Dictionary, © 2010 Douglas Harper
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muscle in in Medicine

muscle mus·cle (mŭs'əl)

  1. A tissue consisting predominantly of contractile cells and classified as skeletal, cardiac, or smooth, the last lacking transverse striations characteristic of the first two.

  2. Any of the contractile organs of the body by which movements of the various organs and parts are effected, and whose fibers are usually attached at each extremity to a bone or other structure by a tendon.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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muscle in in Science
A body tissue composed of sheets or bundles of cells that contract to produce movement or increase tension. Muscle cells contain filaments made of the proteins actin and myosin, which lie parallel to each other. When a muscle is signaled to contract, the actin and myosin filaments slide past each other in an overlapping pattern. ◇ Skeletal muscle effects voluntary movement and is made up of bundles of elongated cells (muscle fibers), each of which contains many nuclei. ◇ Smooth muscle provides the contractile force for the internal organs and is controlled by the autonomic nervous system. Smooth muscle cells are spindle-shaped and each contains a single nucleus. ◇ Cardiac muscle makes up the muscle of the heart and consists of a meshwork of striated cells.

muscular adjective
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Slang definitions & phrases for muscle in

muscle in

verb phrase

To force one's way in, esp into someone's criminal operation: attempt to muscle in on some graft out of his own domain/ afraid you're muscling in on his scam (1929+ Underworld)



  1. A strong-arm man; gorilla: some gowed-up muscle (1929+)
  2. Power; influence; clout: DiBona will have a lot of muscle when it comes to Penn's Landing (1931+)

Related Terms

flex one's muscles, love-muscle

The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D.
Copyright (C) 2007 by HarperCollins Publishers.
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Idioms and Phrases with muscle in

muscle in

Also,muscle in on. Forcibly intrude on or interfere with something, as in The children were determined not to allow the school bully to muscle in, or No more muscling in on our policy decisions! [ ; 1920s ]


In addition to the idiom beginning with
The American Heritage® Idioms Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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