monotonous

Compared meaning: dull, lifeless, or lacking variation (adjective).

比较义项：单调、缺乏变化或活力（形容词）。

• flat

  Describes a single voice, tone, remark or performance as lacking energy or feeling, sounding emotionless or dull in that moment, not necessarily repetitive.

  形容某一次的声音、语气或表现缺乏活力或感情，听起来平淡、没有生气，不一定是因为重复。

  She said 'thanks' in such a flat voice that he wondered if she was upset.

  她用一种很平淡的声音说“谢谢”，他不禁怀疑她是不是不高兴了。

• monotonous 本词

  Describes a voice, sound, job or routine that stays the same without variation over time, becoming boring because it never changes.

  形容声音、工作或日常生活长时间一成不变，因为毫无变化而让人感到乏味。

  The teacher's monotonous voice droned on for an hour, and half the class fell asleep.

  老师用单调的声音讲了一个小时，班上一半的同学都睡着了。

Flat and monotonous both describe something dull, but differently. Flat means a voice, remark, or performance lacks feeling right now. Monotonous means a voice, sound, job, or routine stays the same over time, becoming boring. Flat's other sense, 'apartment', is not compared here.

这两个词在描述声音、语气或表现缺乏生气时意思相近，但侧重不同：flat 强调那一刻缺乏情感和活力，给人平淡、没劲的感觉；monotonous 强调因反复、不变而让人感到乏味。flat 的其他义项（如“公寓”“平的”）不在此比较范围内。