mit ‧ i ‧ ga ‧ tion /ˌmɪtəˈɡeɪʃ ə n, ˌmɪtɪˈɡeɪʃ ə n/ BrE AmE noun [uncountable]
1 . in mitigation law if you say something in mitigation, you try to make someone’s crime or mistake seem less serious or show that they were not completely responsible:
The captain added, in mitigation, that the engines may have been faulty.
2 . formal a reduction in how unpleasant, harmful, or serious a situation is:
His marriage had brought a slight mitigation of the monotony of his existence.