Shikomizue

A Shikomizue (仕込み杖 Japanese prepared cane) is a sword normally concealed inside a cane or walking stick. It is a old fashioned sword that was highly popular amongst the high officals and samurai of Japan during the Meiji period, when the use of a sword was banned in Japan.

One Piece
Brook has been seen wielding one, and Zoro in the anime-only flashback.