flex

American Heritage® Dictionary of the English Language, Fourth Edition

1. v. To bend (something pliant or elastic).
2. v. To bend (a joint).
3. v. To bend (a joint) repeatedly.
4. v. To contract (a muscle, for example).
5. v. To move by muscular control: "Sandy flexes his brow characteristically” ( Scott Turow).
6. v. To exhibit or show off the strength of: "They had spent six years since the lightning Six Day War flexing their invincibility” ( Howard Kaplan).
7. v. To bend: "His hands flexed nervously as he spoke” ( Mary McCarthy).
8. n. Chiefly British Flexible insulated electric cord.
9. n. The act or an instance of flexing; a bending.
10. n. Pliancy; flexibility: "'Resolution' has none of that modern flex we favor, with generous, built-in amounts of 'maybe'” ( Melvin Maddocks).
11. idiom. flex (one's) muscles Informal To exhibit or show off one's strength.

Century Dictionary and Cyclopedia

1. To bend; make a flexure of: specifically said in anatomy of the action of any flexor muscle.
2. n. An obsolete variant of flax.
3. n. A point of contrary flexure or a point of inflexion.

Wiktionary

1. n. uncountable Flexibility, pliancy.
2. n. countable The act of flexing.
3. n. uncountable, chiefly UK Any flexible insulated electrical wiring.
4. n. countable, geometry A point of inflection.
5. v. To bend something.
6. v. To repeatedly bend one of one's joints.
7. v. To move part of the body using one's muscles.
8. v. bodybuilding To tighten the muscles for display of size or strength.

GNU Webster's 1913

1. v. To bend.
2. n. obsolete Flax.

WordNet 3.0

1. v. contract.
2. v. cause (a plastic object) to assume a crooked or angular form
3. v. form a curve
4. n. the act of flexing
5. v. bend a joint
6. v. exhibit the strength of