Mitigant (adjective)
Tending to mitigate.
Mitigant (noun)
Something that mitigates; a lenitive.
Mitigate (verb)
To reduce, lessen, or decrease.
Mitigate (verb)
To downplay.
Wiktionary
Mitigate (verb)
make (something bad) less severe, serious, or painful
“drainage schemes have helped to mitigate this problem”
Mitigate (verb)
lessen the gravity of (an offence or mistake)
“there had been a provocation that mitigated the offence to a degree”
Oxford Dictionary