I still don't think we have any kind of agreed upon definition of "Aiki". We have talked a lot about structure though.
This is why you hear, constantly, that it has to be felt... It's the blind men feeling the elephant... everyone feels something different so it's hard for two people to completely agree on what it is.
today, my definition goes like this:
Aiki is the result of a body that is conditioned to instantly convey forces to and from the ground in a relaxed state, free of muscular force/tension and then manipulate that force both physically (movement) and/or mentally (intent).
and that's just based on what I've felt of the elephant so far and what my training is trying to accomplish. Next week I could meet someone who lets me feel another part of the elephant and my definition could change or at least expand.
Also, I made no mention of the various methods one can condition their body to convey those forces, of which skeletal structure is only one.