Brogue Wiki
The arc of its swing permits you to attack all adjacent enemies simultaneously.

The Axe produces 7-9 (avg 8) damage per hit and requires 15 strength to wield without penalty. The axe is one of several weapons with a special attack property. It is capable of attacking all monsters directly adjacent to the Rogue (within a king's move). A more powerful version of this weapon is the War Axe.

In addition to crowd control in open spaces, a benefit of the axe is that you can attack around a corner, diagonally, if there is another enemy that is a valid target (adjacent, but not around a corner). For instance, if you stand in a doorway surrounded by enemies (see below) you can hit all of them simultaneously, while 2/3 can't retaliate. The axe has lower damage output than a sword, but it also reduces the danger associated with being surrounded.

  • In the following scene, both rats (r) can attack, but the goblins (g) cannot. Nonetheless, the axe will attack each enemy individually, all in a single turn. Note that (in scene 2) with the rats not present, @ does not have a valid target and cannot attack at all.
Scene 1:      g#g           |   Scene 2:      g#g
              r@r           |                  @  
              g#g           |                 g#g
      @ attacks everything  |         @ attacks nothing
       only rats attack @   |         nothing attacks @
Swords: Dagger · Sword · Broadsword — Axes: Axe · War Axe

Polearms: Spear · War Pike — Maces: Mace · War Hammer
Misc: Rapier · Whip · Flail
Ranged: Darts · Incendiary Darts · Javelins