One-handed weapons require only one hand, allowing for Off-hand Items and dual-wielding. However, note that while melee and Mysticality weapons can be wielded together, ranged types can only be doubled up with other ranged weapons.
All crossbows, slingshots, banjos, guitars, pistols, and accordions are ranged weapons. All other items are considered melee/Mysticality weapons unless otherwise noted.
The Disembodied Hand familiar can equip all one-handed weapons (with the exception of Chefstaves), regardless of level requirements, and convey the weapon's effects to you.