Wiktionary
prep.phr. (context idiomatic English) exactly, precisely.
WordNet
adj. being precisely to a prescribed or specified criterion; "his guess was on the nose"; "the prediction for snow was right on the button" [syn: on the nose]
adv. just as it should be; "`Precisely, my lord,' he said" [syn: precisely, exactly, on the nose, on the dot]
Usage examples of "on the button".
That they haven't been used might mean they haven't been found yet, or that the technicians have their finger on the button, just waiting for their big moment.
Reluctantly he clicked on the button and instantly the screen filled with a stunning video image that took his breath away.
Again gently, he moved the heavy rolling chair inches to the left and centered his eyes on the button.
His predictions checked out right on the button-if he hadn't died, the life insurance companies would have been ruined.
In front of the map screen a youngish man sat quietly in a chair, a pear-shaped switch in his hand, his thumb lightly resting on the button.