Re: Ueshiba, Takeda, & 1921 - What happened?
As far as I know, it's the first time that it was used in a "generic" sense - jujutsu, bojutsu, aikijutsu. But the term "aiki" is quite old. for example, Toda-ha Buko-ryu uses the term "aiki no koto" to refer to the kusarigama vs. naginata kata that are middle level techniques in the school. As best as I can tell, "aiki," in this case, means "fitting together," something that is required to make the kata work, a particular point of study at middle level.