Concise Bible Dictionary:

This term is used to express the present attitude and testimony of God toward man consequent on the declaration of God’s righteousness in the death of Christ. The state of man which was obnoxious to the holiness of God by reason of sin has been removed in the cross. Hence the believer is justified by faith, and has peace (peace of conscience) with God through the Lord Jesus Christ (Rom. 5:11Therefore being justified by faith, we have peace with God through our Lord Jesus Christ: (Romans 5:1)). Christ made peace through the blood of the cross (col. 1:2020And, having made peace through the blood of his cross, by him to reconcile all things unto himself; by him, I say, whether they be things in earth, or things in heaven. (Colossians 1:20)); and to the Christian God is “the God of peace,” and the Lord Jesus is “the Lord of peace.” He also is peace between believers, having on the cross broken down the barrier between Jew and Gentile (Eph. 2:14-1514For he is our peace, who hath made both one, and hath broken down the middle wall of partition between us; 15Having abolished in his flesh the enmity, even the law of commandments contained in ordinances; for to make in himself of twain one new man, so making peace; (Ephesians 2:14‑15)).
When the Lord Jesus left the earth He left to the disciples peace, and said, “My peace I give unto you.” Peace is also spoken of as the state of heart in which a believer is kept in regard of circumstances. The record in the Old Testament is, “Thou wilt keep him in perfect peace (peace, peace, margin) whose mind is stayed on Thee, because he trusteth in Thee” (Isa. 26:33Thou wilt keep him in perfect peace, whose mind is stayed on thee: because he trusteth in thee. (Isaiah 26:3)). The Christian makes his requests known unto God, and the peace of God that passeth all understanding keeps his heart and mind through Christ Jesus—peace of heart (Phil. 4:6-76Be careful for nothing; but in every thing by prayer and supplication with thanksgiving let your requests be made known unto God. 7And the peace of God, which passeth all understanding, shall keep your hearts and minds through Christ Jesus. (Philippians 4:6‑7)). Blessed privilege! and what a contrast to “There is no peace, saith my God, to the wicked” (Isa. 57:2121There is no peace, saith my God, to the wicked. (Isaiah 57:21)). The Lord Jesus will, in the future, among His other titles, be hailed as PRINCE OF PEACE (Isa. 9:66For unto us a child is born, unto us a son is given: and the government shall be upon his shoulder: and his name shall be called Wonderful, Counsellor, The mighty God, The everlasting Father, The Prince of Peace. (Isaiah 9:6)).

Strong’s Dictionary of Greek Words:

from 1515; pacific; by implication, salutary
KJV Usage: