a sword
Examples
Never give a sword to a man who can't dance.
Poetry is a sword of lightning, ever unsheathed, which consumes the scabbard that would contain it.
The world may end up under a Sword of Damocles on a tightrope over the abyss.
A sword in the hands of a drunken slave is less dangerous than science in the hands of the immoral.
Never give a child a sword.
Money is sharper than a sword.