Webster's Dictionary 
(1): ( n.) The act of sending back.
(2): ( n.) The act of remitting, surrendering, resigning, or giving up.
(3): ( n.) Discharge from that which is due; relinquishment of a claim, right, or obligation; pardon of transgression; release from forfeiture, penalty, debt, etc.
(4): ( n.) Diminution of intensity; abatement; relaxation.
(5): ( n.) A temporary and incomplete subsidence of the force or violence of a disease or of pain, as destinguished from intermission, in which the disease completely leaves the patient for a time; abatement.
(6): ( n.) Act of sending in payment, as money; remittance.
King James Dictionary 
REMIS'SION, n. L. remissio, from remitto, to send back.
1. Abatement relaxation moderation as the remission of extreme rigor. 2. Abatement diminution of intensity as the remission of the sun's heat the remission of cold the remission of close study or of labor. 3. Release discharge or relinquishment of a claim or right as the remission of a tax or duty. 4. In medicine, abatement a temporary subsidence of the force or violence of a disease or of pain, as distinguished from intermission, in which the disease leaves the patient entirely for a time. 5. Forgiveness pardon that is, the giving up of the punishment due to a crime as the remission of sins. Matthew 26 . Hebrews 9 . 6. The act of sending back. Not in use.
Holman Bible Dictionary 
remission Esther 2:18 forgiveness Romans 3:25 aphesis Mark 1:4 Luke 3:3 Luke 24:47 Acts 2:38 Acts 5:31 Matthew 26:28 Hebrews 10:17-18 Acts 5:31 Acts 10:43 Luke 24:47 Acts 2:38 Hebrews 10:18 Romans 3:25
Morrish Bible Dictionary 
This is used in the sense of 'forgiveness.' The forgiveness or remission of sins is through faith in the Lord Jesus Christ and on the ground of His sacrificial death. Acts 10:43; Acts 13:38; Romans 3:25; 1 Corinthians 15:3 . See FORGIVENESS.
Hastings' Dictionary of the New Testament