H3722 kāp̱ar cover, forgive, atone, expiate

Baker & Carpenter, “A verb meaning to cover, to forgive, to expiate, to reconcile. This word is of supreme theological importance in the Old Testament as it is central to an Old Testament understanding of the remission of sin. At its most basic level, the word conveys the notion of covering but not in the sense of merely concealing. Rather, it suggests the imposing of something to change its appearance or nature. It is therefore employed to signify the cancellation or “writing over” of a contract (Isa. 28:18); the appeasing of anger (Gen. 32:20[21]; Prov. 16:14); and the overlaying of wood with pitch so as to make it waterproof (Gen. 6:14). The word also communicates God’s covering of sin. Persons made reconciliation with God for their sins by imposing something that would appease the offended party (in this case the Lord) and cover the sinners with righteousness (Ex. 32:30; Ezek. 45:17; cf. Dan. 9:24). In the Old Testament, the blood of sacrifices was most notably imposed (Ex. 30:10). By this imposition, sin was purged (Ps. 79:9; Isa. 6:7) and forgiven (Ps. 78:38). The offenses were removed, leaving the sinners clothed in righteousness (cf. Zech. 3:3, 4).* Of course, the imposition of the blood of bulls and of goats could never fully cover our sin (see Heb. 10:4), but with the coming of Christ and the imposition of His shed blood, a perfect atonement was made (Rom. 5:9–11).” [Warren Baker and Eugene E. Carpenter, The Complete Word Study Dictionary: Old Testament (Chattanooga, TN: AMG Publishers, 2003), 521.]

*Don: Here I’d cite Rom 3.25 in saying the offenses weren’t removed then, in OT times, but left unpunished until they were actually removed by “the Lamb of God who takes away the sin” as in Jn 1.29.