mid-13c. (implied in botouner "button-maker"), from O.Fr. boton (Fr. bouton) "a button, bud" (12c.), from bouter, boter "to thrust" (see butt (v.)). Thus a button is, etymologically, something that pushes up, or thrusts out. The verb is late 14c.
The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Idioms and Phrases with on the button
Exactly right, precisely, as in Her review of the book was right on the button, or We're supposed to be there at six o'clock on the button. This term may come from boxing, where a punch on the button means “a punch on the chin.”
[ ; c. 1900