bokken
A lethal kendo practice sword made of solid, heavy wood. It's shaped and balanced like a katana.
Bokken are normally used for solo training, not for sparring. For that, the shinai is used, as sparring with a bokken will usually lead to broken bones... or worse.
Legendary samurai swordmaster Miyamoto Musashi is said to have fought and killed katana-wielding rival samurai by using just a bokken against them.