General synonyms:
* Boring: Lacking interest or excitement.
* Tedious: Tiresome or monotonous.
* Monotonous: Unvarying and lacking in interest.
* Bland: Lacking strong flavor or excitement.
* Uninteresting: Not engaging or captivating.
* Uninspiring: Failing to stimulate or motivate.
* Humdrum: Ordinary and lacking in excitement.
* Tiresome: Causing weariness or fatigue.
* 乏味 (fá wèi) (Chinese)
Synonyms for "dull" in the sense of "not sharp":
* Blunt: Lacking sharpness or a point.
* Unpointed: Having no point.
* Obtuse: Not sharp or pointed.
* Rounded: Having a smooth, rounded shape.
* Dull-edged: Having a blunt edge.
Synonyms for "dull" in the sense of "not bright":
* Dim: Lacking in brightness.
* Dark: Lacking in light.
* Gloomy: Dark and depressing.
* Gray: Lacking color or brightness.
* Muddy: Cloudy or unclear.
Synonyms for "dull" in the sense of "not lively or energetic":
* Sluggish: Slow-moving or inactive.
* Lethargic: Lacking energy or enthusiasm.
* Apathetic: Showing or feeling no interest, enthusiasm, or concern.
* Listless: Lacking energy or enthusiasm.
Choose the synonym that best fits the specific context you are writing or speaking about.