Tonfa (4e Equipment)
From D&D Wiki
Military Melee Weapons
A tonfa is a bar of wood, roughly a half a foot longer the length of an adult, human forearm, and a hilt on the shaft of the wood itself, usually 6 inches from an end.
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.
A defensive weapon grants you a +1 bonus to AC while you wield the defensive weapon in one hand and wield another melee weapon in your other hand. Wielding more than one defensive weapon does not increase this bonus. To gain this benefit, you need not attack with the defensive weapon, but you must be proficient with it.