If someone lightens a situation, they make it less serious or less boring. Anthony felt the need to lighten the atmosphere
If your attitude, or mood lightens, or if someone or something lightens it, they make you feel more cheerful, happy, and relaxed. As they approached the outskirts of the city, Ella's mood visibly lightened The sun was streaming in through the window, yet it did nothing to lighten his mood
If you lighten something, you make it less heavy. It is a good idea to blend it in a food processor as this lightens the mixture He pulled the lightened sled with all his strength
To make light or clear; to light; to illuminate; as, to lighten an apartment with lamps or gas; to lighten the streets