- 1(informal) to begin to smoke a cigarette They all lit up as soon as he left the room. He sat back and lit up a cigarette.
- 2to become or to make something become bright with light or colour There was an explosion and the whole sky lit up. The night sky was lit up with fireworks.
- 3if somebody’s eyes or face light up, or something lights them up, they show happiness or excitement His eyes lit up when she walked into the room. A smile lit up her face.