The word nyu-bachi (mortar) is seen in Shogaku-Kagaku-sho, a book of chemistry in 1874 but its etymon is unknown. The word ru-bo (nyu-bachi in Japanese) is seen in several ancient books in medicine, art and literature, from the 5th to 18th century. In these books, the usage of ru-bo is written as crush the solids. In 1874, the translator Tosen Hoda did not make a new Japanese word for mortar but used the ancient Chinese word ru-bo (nyu-bachi). This was because he found that the usage of European mortar is the same as that of the ancient Chinese ru-bo. The word nyu has several meanings. The etymon of the word nyu-bachi comes from the female breast nyu, not liquid nyu. The reasons are as follows : 1) the usage of ru-bo (nyu-bachi) is for solids, not liquids, and 2) the word bo (bachi) means hemisphere bowl. It may stand for a kind of humor in ancient Chinese male society.