A magical weapon is a tool consecrated to and used in Magic.

Alistar Crowley on the Magical Weapons in Magick in Theory and Practice - Book 4, wrote:

"The Magician works in a Temple; the Universe, which is (be it remembered!) conterminous with himself. In this Temple a Circle is drawn upon the floor for the limitation of his working. This circle is protected by divine names, the influences on which he relies to keep out hostile thoughts. Within the circle stands an Altar, the solid basis on which he works, the foundation of all. Upon the Altar are his Wand, Cup, Sword, and Pantacle, to represent his Will, his Understanding, his Reason, and the lower parts of his being, respectively. On the Altar, too, is a phial of Oil, surrounded by a Scourge, a Dagger, and a Chain, while above the Altar hangs a Lamp. The Magician wears a Crown, a single Robe, and a Lamen, and he bears a Book of Conjurations and a Bell."

"The oil consecrates everything that is touched with it; it is his aspiration; all acts performed in accordance with that are holy. The scourge tortures him; the dagger wounds him; the chain binds him. It is by virtue of these three that his aspiration remains pure, and is able to consecrate all other things. He wears a Crown to affirm his lordship, his divinity; a robe to symbolize silence, and a lamen to declare his work. The book of spells or conjurations is his magical record, his Karma. In the East is the Magick Fire, in which all burns up at last."

The weapons each have a element associated with them. The weapons also relate to the four suits of the Minor Arcan of the Tarot.

Wand - Fire
Cup - Water
Sword - Air
Pentacle - Earth (in some Tarot pack this is Coins)