The Sword of the Zephyr is one of Thaumcraft's "elemental tools", offering limited flight, group attack, and protection against missiles.
When attacking, this sword can attack several opponents that are close to each other. It can even include some enemies that would otherwise be out of reach, but at least one mob needs to be hit in the usual fashion. This will cost extra durability.
The greater powers of the sword appear when it is used to block: The user will be surrounded by circling winds. Not only will these push away mobs, missiles, and loose items, but the wielder will slowly rise into the air, until they reach a ceiling or release the block. While flying in this manner, they can move horizontally, at the usual speed for moving while blocking. This also serves to halt a fall, which is handy once the player has floated up to some dangerous height, or simply wants to descend into a ravine or somesuch.
Blocking will consume durability at a slow but steady rate. Note that if the sword has Repair, each time a point of durability is restored, the sword will briefly "unblock", and the player will fall briefly. This will not prevent flight, but will make it somewhat uneven.