Armor in Chinese / Japanese...

鎧 is a simple way to write armor/armour in Chinese, Japanese Kanji, and old Korean Hanja.

This can also be Yoroi (a Japanese place name). It can also refer to mail as chain mail.

柔術 has been somewhat incorrectly spelled and pronounced “Jujitsu” for some time in the English-speaking world. The correct Japanese Romaji is Jujutsu or Juujutsu.

A little background on the word: By combining the Kanji pronounced “Ju” (which means flexible, pliable, gentle, yielding) with the Kanji pronounced “Jutsu” (which means art or technique), we get a meaning that can be translated as “flexible technique,” “gentle art” or “yielding technique.”
柔術 does make sense in Chinese as well, although pronounced “rou shu” in China.

The Jujutsu system has a history in Japan that started well before the 1600s. Some see this style as a variation of the “Empty Hand Method” (Karate-do). Even the samurai of old used some Jujutsu methods in defending themselves with their unarmed hands against weapons that could pierce their heavy armor.

There are convoluted relationships between various schools and systems of martial arts, but it's generally accepted that Jujutsu led to the development of Judo and a few other variations.