General opposites:
* Dull: Lacking in excitement, interest, or energy.
* Quiet: Characterized by a lack of noise or activity.
* Bland: Lacking strong features or characteristics, boring.
* Stagnant: Not moving or developing.
* Inert: Lacking in energy or movement.
Opposites related to specific aspects of liveliness:
* Somber: Gloomy, serious, and sad. (Opposite of lively in terms of mood)
* Sluggish: Slow-moving and lacking in energy. (Opposite of lively in terms of activity)
* Uninspiring: Not motivating or exciting. (Opposite of lively in terms of inspiration)
* Monotonous: Repetitive and boring. (Opposite of lively in terms of variety)
The best opposite word depends on the specific context and what aspect of "lively" you want to contrast.