What is "in arms"

Arms \Arms\, n. pl. [OE. armes, F. arme, pl. armes, fr. L. arma, pl., arms, orig. fittings, akin to armus shoulder, and E. arm. See Arm, n.]

1. Instruments or weapons of offense or defense.

   He lays down his arms, but not his wiles.
   --Milton.

   Three horses and three goodly suits of arms.
   --Tennyson.

2. The deeds or exploits of war; military service or science. ``Arms and the man I sing.''
   --Dryden.

3. (Law) Anything which a man takes in his hand in anger, to strike or assault another with; an aggressive weapon.
   --Cowell. Blackstone.

4. (Her.) The ensigns armorial of a family, consisting of figures and colors borne in shields, banners, etc., as marks of dignity and distinction, and descending from father to son.

5. (Falconry) The legs of a hawk from the thigh to the foot.
   --Halliwell.

   Bred to arms, educated to the profession of a soldier.

   In arms, armed for war; in a state of hostility.

   Small arms, portable firearms known as muskets, rifles, carbines, pistols, etc.

   A stand of arms, a complete set for one soldier, as a musket, bayonet, cartridge box and belt; frequently, the musket and bayonet alone.

   To arms! a summons to war or battle.

   Under arms, armed and equipped and in readiness for battle, or for a military parade.

   Arm's end,

   Arm's length,

   Arm's reach. See under Arm.