Definitions

1. noun

a group of fibers or a fiber forming part of the structure of an animal, especially a human.

“The athlete strained her muscle while lifting the heavy weights.”

2. noun

a particular part of an animal’s body, such as the biceps or triceps.

“She worked out to build her bicep muscle.”

3. verb

to strengthen or build up a muscle or muscles, typically through exercise.

“He muscles up for the upcoming marathon by running every day.”