Lessen/ˈlesn/ Definition 1 of 2Pro Tip 1/3Action Oriented Use 'lessen' when describing an intentional action to reduce something. She took measures to lessen environmental damage. Pro Tip 2/3Mitigate Effects 'Lessen' is often used when talking about making negative effects not as severe. Wearing a helmet can lessen the chance of a head injury. Pro Tip 3/3Progressive Change Use 'lessen' to imply a gradual reduction over time, rather than immediate. Her attention to detail lessened as she grew tired.