Weapon, n. — Webster enters it under “weapon”
Etymology: [OE. wepen, AS. w; akin to OS. w, OFries. w, w, D. wapen, G. waffe, OHG. waffan, wafan, Icel. vapn, Dan. vaaben, Sw. vapen, Goth. w, pl.; of uncertain origin. Cf. Wapentake.]
1. An instrument of offensive of defensive combat; something to fight with; anything used, or designed to be used, in destroying, defeating, or injuring an enemy, as a gun, a sword, etc. The weapons of our warfare are not carnal. 2 Cor. x. 4. They, astonished, all resistance lost, All courage; down their idle weapons dropped. Milton.
2. Fig.: The means or instrument with which one contends against another; as, argument was his only weapon. "Woman's weapons, water drops." Shak.
3. (Bot.)
A thorn, prickle, or sting with which many plants are furnished. Concealed weapons. See under Concealed. -- Weapon salve, a salve which was supposed to cure a wound by being applied to the weapon that made it. [Obs.] Boyle.
Shades of meaning
Fernald has no entry of its own for weapons; he lists it under arms.
Where he writes about it:
Those things by which pacific and industrial operations are performed are alone properly called tools, those designed for warlike purposes being designated weapons. — from tool