Easton's Bible Dictionary
The purchase back of something that had been lost, by the payment of a ransom. The Greek word so rendered is apolutrosis, a word occurring nine times in Scripture, and always with the idea of a ransom or price paid, i.e., redemption by a lutron (see Matthew 20:28; Mark 10:45). There are instances in the LXX. Version of the Old Testament of the use of lutron in man's relation to man (Leviticus 19:20; 25:51; Exodus 21:30; Numbers 35:31, 32; Isaiah 45:13; Proverbs 6:35), and in the same sense of man's relation to God (Numbers 3:49; 18:15).
There are many passages in the New Testament which represent Christ's sufferings under the idea of a ransom or price, and the result thereby secured is a purchase or redemption (Comp. Acts 20:28; 1 Corinthians 6:19, 20; Galatians 3:13; 4:4, 5; Ephesians 1:7; Colossians 1:14; 1 Timothy 2:5, 6; Titus 2:14; Hebrews 9:12; 1 Peter 1:18, 19; Revelation 5:9). The idea running through all these texts, however various their reference, is that of payment made for our redemption. The debt against us is not viewed as simply cancelled, but is fully paid. Christ's blood or life, which he surrendered for them, is the "ransom" by which the deliverance of his people from the servitude of sin and from its penal consequences is secured. It is the plain doctrine of Scripture that "Christ saves us neither by the mere exercise of power, nor by his doctrine, nor by his example, nor by the moral influence which he exerted, nor by any subjective influence on his people, whether natural or mystical, but as a satisfaction to divine justice, as an expiation for sin, and as a ransom from the curse and authority of the law, thus reconciling us to God by making it consistent with his perfection to exercise mercy toward sinners" (Hodge's Systematic Theology).
Noah Webster's New International Dictionary of the English Language
(n.) The recovery of what is promised; as, the redemption of a bond.