I.  The Verb.

 1.  metanoeo = to change one's mind, always for the better, and morally. Because of this it is often used in the Imperative (Matthew 3:2; 4:17. Acts 2:38; 3:19). Not merely to forsake sin, but to change one's apprehension regarding it. It occurs thirty-four times. It answers to the Latin resipisco = to recover one's senses, to come to one's self.

 2.  metamelomai = to regret; to have after-care or annoyance at the consequences of an act of sin rather than a deep regret at the cause from want of not knowing better. Hence it is never used in the Imperative. It occurs six times, and in each case (except Matthew 21:29, 32) never in the real Biblical sense of "repentance toward God". It is from meta = after, and melo = to be an object of care. See notes on 2Corinthians 7:8 and 10.

It is used of Judas Iscariot (Matthew 27:3); negatively of Paul's regret (2Corinthians 7:8); and of God (Hebrews 7:21).
  The Noun, metameleia, is not used in the N.T.
 
II.  The Noun.
 
  metanoia = a real change of mind and attitude toward sin itself, and the cause of it (not merely the consequences of it), which affects the whole life and not merely a single act. It has been defined as a change in our principle of action (Greek nous) from what is by nature the exact opposite. It occurs twenty-four times, and except Hebrews 12:17 is a real "repentance toward God". It is associated with the work of the Holy Spirit, and is connected with the remission of sins and the promises of salvation.
 
III.  The Negative Adjective, ametameletos, is used twice, namely, Romans 11:29, and 2Corinthians 7:10.