mitigation

[OE. mitigacioun, F. mitigation, fr. L. mitigatio.]
The act of mitigating, or the state of being mitigated; abatement or diminution of anything painful, harsh, severe, afflictive, or calamitous; as, the mitigation of pain, grief, rigor, severity, punishment, or penalty.

Syn. -- Alleviation; abatement; relief.

noun

Freedom, especially from pain: alleviation, assuagement, ease, palliation, relief. See increase/decrease.

The noun has 2 meanings:

Meaning #1: to act in such a way as to cause an offense to seem less serious
  Synonyms: extenuation, palliation

Meaning #2: a partial excuse to mitigate censure; an attempt to represent an offense as less serious than it appears by showing mitigating circumstances
  Synonym: extenuation