A tachi (太刀) was a type of traditionally made Japanese sword (nihontō) worn by the samurai class of feudal Japan. The tachi style of swords preceded the development of the katana and were primarily used on horseback. Tachi and katana generally differ in:
Curvature: tachi tend to be more curved (both hilt and blade).
How they are worn: tachi is worn suspended from the belt with its cutting edge downward, while the katana is thrust through the belt with its cutting edge upward (see reference).
Length: tachi tend to be longer than the katana.
Hilt: while katana always have a rayskin-wrapped hilt with silk overwrapping, tachi sometimes only have the rayskin wrapping, though this is far from universal.
See also
Chokutou, straight swords, were also called tachi, but written as 大刀
