Webster’s Revised Unabridged Dictionary · 1913
Flex
Flex (flĕks), v. t. [imp. & p. p. Flexed; p. pr. & vb. n. Flexing.] [L. flexus, p. p. of flectere to bend, perh. flectere and akin to falx sickle, E. falchion. Cf. Flinch.] To bend; as, to flex the arm.
Flex, n. Flax. [Obs.] Chaucer.