[flex] vb [L flexus, pp. of flectere to bend] vt (ca. 1521) 1: to bend esp. repeatedly
2. a: to move muscles so as to cause flexion of (a joint) b: to move or tense (a muscle) by contraction ~ vi: bend -- flex one's muscles : to demonstrate one's strength "an exaggerated need to flex his political muscles --J. P. Lash"
[2]flex n [short for flexible cord] (1905) chiefly Brit: an electric cord [3]flex n (ca. 1934): an act or instance of flexing