Monk unarmed strike
Simple one-handed melee weaponDamage
Off-Hand (An off-hand weapon is light enough that you can hold it and attack effectively with it while holding a weapon in your main hand. You can’t attack with both weapons in the same turn, unless you have a power that lets you do so, but you can attack with either weapon.
Unarmed (When you punch, kick, elbow, knee, or even head butt an opponent, you’re making an unarmed strike. A simple unarmed attack is treated as an improvised weapon. Creatures that have natural weapons such as claws or bite attacks are proficient with those natural weapons.
Published in Player's Handbook 3, page(s) 63.