Not regret — a fundamental change of how a person thinks
Metanoia is the New Testament word for repentance, and it is not the same as metamelomai — which is regret, the feeling of being sorry. Metanoia is meta + nous: an after-mind, a turned mind, a mind made new. It belongs in the same family of verbs as metamorphoo (transformed by the renewing of your mind), anakainosis (renewing), and ananeoo (made fresh). What it is not is mere remorse. What it is is a different intellect altogether.