muscle

the english word "muscle" entered the language in the late 14th century from old french muscle, which itself derived from latin musculus, meaning "a muscle" and literally "little mouse." this whimsical anatomical metaphor likely arose from the perceived resemblance of a flexing muscle, particularly the bicep, to the shape and movement of a mouse under the skin. the latin musculus is a diminutive of mus (mouse), a term with ancient indo-european roots. over time, the primary meaning shifted entirely to the anatomical sense, while the connotation of strength and power developed as a figurative extension of its physical function.

the word is a simplex form. it is a loanword from latin musculus, meaning "little mouse" and "muscle." the latin word is a diminutive of mus ("mouse").