Since ki is used in the Japanese language as part of hundreds of idioms ( see Jun's list below ) and O'Sensei undoubtedly knew this, maybe the ki in Aikido is meant to be an open ended idiom, no single definition but many.
Erm... most japanese people, and by most I mean 99.999% out there don't give a second thought as to the definition of "Ki" within their language. I'd say anyone reading that deep into it is reading something that isn't there.
What would, and does make sense is that "Aiki"do comes from the term "Aiki" that his teacher Takeda used. In fact it was Takeda who introduced the term and made it well known in that time period.
Sometimes the simplest explanations are the best ^^;