Noun
A long, large Japanese sword.
A long Japanese sword built like the katana but longer (about 4 to 6 feet long), for combat on horseback.
Source: en.wiktionary.orgHe is referring to the katana in this, and refers to the nodachi and the odachi as "extra-long swords". Source: Internet
Citizens are not allowed to possess an odachi unless it is for ceremonial purposes. Source: Internet