flexor(n = noun.body) flexor muscle - a skeletal muscle whose contraction bends a joint;
is a kind of skeletal muscle, striated muscle
Antonym: extensor

   A muscle which bends or flexes any part; as, the flexors of the arm or the hand; -- opposed to extensor. [1913 Webster]

flexor, n. (in full flexor muscle) a muscle that bends part of the body (cf. EXTENSOR).

Etymology:
mod.L (as FLEX(1))

flexor muscle