mitigating circumstance

noun

: a circumstance in the commission of an act that lessens the degree of criminal culpability

was convicted of manslaughter rather than murder because of mitigating circumstances

also : a circumstance or factor relating to an offense or defendant that does not bear on the question of culpability but that receives consideration by the court especially in lessening the severity of a sentence

the mitigating circumstance of the defendant's terminal illness

compare aggravating circumstance