Толковый словарь английского языка - flex

I. verb Etymology: Latin ~us, past participle of flectere to bend Date: circa 1521 transitive verb to bend especially repeatedly, 2. to move muscles so as to cause ~ion of (a joint), to move or tense (a muscle) by contraction, use, demonstrate , intransitive verb bend, II. noun Etymology: short for ~ible cord Date: 1905 an electric cord, III. noun Date: circa 1934 an act or instance of ~ing