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 (Matt. 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 annoyances 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 time, and in each case (except Matt. 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 2Cor. 7:8 and 10.  It is used of Judas Iscariot (Matt. 27:3); negatively of Paul's regret (2Cor. 7:8); and of God (Heb. 7:21).

The Noun, metameleia, is not used in the N.T.

1.  metanoia = a real change of mind and attitude toward sin itself, and the cause of it (not merely the consequence 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 (Gr. nous) from what is by nature the exact opposite.  It occurs twenty-four times, and except Heb. 12:17 is a real "repentance toward God".  It is associated with the word of the Holy Spirit, and is connected with the remission of sins and the promises of salvation.