Rune

Rune is a spell which can only be learned by Wizards who read the Rune Spellbook.

It cannot be cast on a weapon that has been sharpened, poisoned, or has a natural ac modifier. Once a weapon has been runed it cannot be sharpened.

When you cast rune, you can either specify a rune to imprint upon the weapon, or you can delve the weapon. Delving will give you some insight into what effect the different runes will have upon this specific weapon, but be aware that delve can return false results.

The runes you can imprint upon a weapon are: ka yal vi rin boh chy era to nol zor.

When a rune character is imprinted upon a weapon, it can become one of the following:

Rune of Battle: -3 ac
Rune of Defense: -5 ac
Rune of Invulnerabiity: -10 ac
Rune of Sickliness: -2 con
Rune of Confusion: -2 wis
Rune of Weakness: -5 dr
Rune of Striking: increased min & avg damage
Rune of Vanquishing: increased min, avg, & max damage

Note that it's also possible for a rune to have no effect on a weapon.

If you'd like to spoil the fun of figuring out rune works for yourself, you can check out this Rune Chart.