Mitigate : make (something bad) less severe, serious, or painful.Stagnate : (of water or air) cease to flow or move; become stagnant.Suffer : experience or be subjected to (something bad or unpleasant).Aggravate : make (a problem, injury, or offence) worse or more serious.Instigate : incite someone to do something, especially something bad.Antonym of Mitigate is Aggravate