I've heard for a long time that Tomiki-sensei called it "fitting".
A meeting of energy and fitting together harmoniously (meaning, I think, not clashing, good timing, etc.)
Another aspect is "instant victory", taking someone's balance, initiative, etc. at the time of "fitting" that happens at first touch.
First touch may be at some distance, affecting an attackers intent and leading their mind...
aiki-DO is another thing.