The Etymology of "Atone"
From Amy Welborn's post entitled The body's forgotten ally:

St. Thomas More coined the English word “atone” by combining two words, “at one,” to produce one meaning “to reconcile opposing sides of a conflict.”

I always assumed the word was Latinate in origin, but realizing their was no Spanish equivalent, went to AskOxford.com, the searchable online version of the Oxford English Dictionary, "[t]he definitive record of the English language," which confirmed this origin if not its originator.