From katallasso; exchange (figuratively, adjustment), i.e. Restoration to (the divine) favor -- atonement, reconciliation(-ing).
see GREEK katallasso
1. exchange; of the business of money-changers, exchanging equivalent values ((Aristotle, others)). Hence,
2. adjustment of a difference, reconciliation, restoration to favor, (from Aeschylus on); in the N. T., of the restoration of the favor of God to sinners that repent and put their trust in the expiatory death of Christ: 2 Corinthians 5:18f; with the genitive of the one received into favor, τοῦ κόσμου (opposed to ἀποβολή), Romans 11:15; καταλλαγήν ἐλάβομεν, we received the blessing of the recovered favor of God, Romans 5:11; with the genitive of him whose favor is recovered, 2 Macc. 5:20. (Cf. Trench, § lxxvii.)