Ai: match, fit, suit, join, combine, unite, coincide, agree.
Ki: air, atmosphere, spirit, mind, heart, will, intention, feelings, a mood, nature, a disposition, attention, care, a sign, an indication.
These are basic, no frills definitions. I find that it is best to start from the most obvious and mundane. These will not provide the final answer, and can likely be argued in any direction. But, whatever phenomena people, Morihei included, had in mind, I doubt seriously that the characters ai and ki were randomly selected.
Dan Harden wrote:
Drawing a circle and explaining Aiki is opposing powers.
The mysteries of aiki are revealed in dual opposing spirals.
I'm curious. Can anyone provide the source and brief explanation behind the translation for the above quotes? I can't remember off the top of my head where Morihei used that language.