Lilt as a musical or rhythmic quality:
* Monotony: This suggests a lack of variation or rhythm.
* Dullness: This implies a lack of energy or vibrancy.
* Flatness: This describes a lack of musicality or a boring sound.
Lilt as a light, graceful movement:
* Clumsiness: This describes awkward and ungainly movement.
* Heaviness: This refers to a lack of lightness and grace.
* Stiffness: This implies a lack of fluidity and ease.
Lilt as a cheerful or playful quality:
* Gloominess: This suggests sadness or seriousness.
* Seriousness: This implies a lack of playfulness or lightheartedness.
* Dourness: This describes a stern or unsmiling demeanor.
The best opposite word for "lilt" will depend on the specific context and the meaning you want to convey.