The word (at-one-ment) is used but once in the New Testament (Rom. 5:11), and there it means expressly and exactly reconciliation. This is proved thus: the same Greek word in the next verse, carrying the very same meaning, is translated reconciliation. Now, people continually mix two ideas when they say atonement: One is, that of the expiation for guilt provided in Christ's sacrifice. The other is, the individual reconciliation of a believer with his God, grounded on that sacrifice made by Christ once for all, but actually effectuated only when the sinner believes and by faith. The last is the true meaning of atonement, and in that sense every, atonement (at-one-ment), reconciliation, must be individual, particular, and limited to this sinner who now believes. There have already been just as many atonements as there are true believers in heaven and earth, each one individual.R. L. Dabney, The Five Points of Calvinism (Harrisonburg, VA: Sprinkle Publications, 1992), 60.
Dabney got the atonement word right, but I wish he got the "redemption" word right as well. I believe he erred on the use of that word.