Re: Defining the word "Aiki" and looking at the phenomenon it describes.
I suggest that these are not different definitions of aiki, but causes and effects, provided one starts with the premise that C is the definition of aiki.
If aiki is a body ability, that once acquired gives it's practitioner great physical power, making them seem unmovable and strangely forceful. then it stands to reason that once acquired, it would allow your body to automatically adapt to movements and changes made by an attacker/opponent, that make the opponent feel strange, weak, unable to adapt to you.
It would also stand to reason that two equally skilled opponents when looking for an opening would be in a situation created by two people, of equal skill wherein neither can make a successful attack, locking them in a stand off and that if one person was more skilled than his opponent that he would have ability to understand, blend with, lead and manipulate the mind/intention of his opponent.
In essence, it's like the blind men and the elephant, each describing a different animal because they each got hold of a different part.