If a place or event livens up, or if something livens it up, it becomes more interesting and exciting. How could we decorate the room to liven it up? The multicoloured rag rug was chosen to liven up the grey carpet The arena livens up only on Saturdays and Sundays when a flea market is open there
If people liven up, or if something livens them up, they become more cheerful and energetic. Talking about her daughters livens her up George livens up after midnight, relaxing a little. = perk up