The word is believed to have been left by Kyuzo MIFUNE, a 10th dan judo wrestler in the early days of The Kodokan Judo Institute, who was famous for creating the kuki nage (the air throw).
空気投げを編み出したことで有名な講道館初期の柔道家、三船久蔵十段が残した言葉であるといわれる。