Power
c.1300, from Anglo-Fr. pouair, O.Fr. povoir, noun use of the infinitive in O.Fr., "to be able," earlier podir (842)...
-Harvard Etymology online dictionary
The word's origins are quite in line with Headlong's assessment. However, I don't want to solely address the reactive part of the art. There are brief moments of offensive defense in Aikido. The floating throws of Niju-san beautifully display this. In these moments of time we have elected to drive our hand through Ukei's face or "upper solar-plexus" as some of my colleagues refer to it. The drives to the face aren't half-hearted. The attacks are body drops.
And here Headlong's point comes up again, the way in which we commit to these attacks allows us to still be responsive! These brief moments of actual commitment coupled with responsiveness are truly what have been some of the more interesting moments to me. I enjoy how easily you can tell when someone has committed and is floating as opposed to not having one of the two parts.
Summary
-Hand to the face + floating foot + committed drop= interesting.
-Balanced
