fairly

Compared meaning: to a moderate degree, quite (adverb).

比较义项：表示程度的“相当／有点”（副词）。

• pretty

  Informal and mainly spoken; feels stronger and more casual than fairly or somewhat, and sounds out of place in formal writing.

  非正式，多用于口语；比 fairly 和 somewhat 语气更强、更随意，用在正式书面语中会显得不合适。

  It's pretty late already, so we should probably head home now.

  现在已经相当晚了，我们大概应该回家了。

• somewhat

  More formal and often written; commonly precedes comparative forms or verbs of change, which pretty and fairly cannot naturally do.

  更正式，多用于书面语；常放在比较级或表示变化的动词前，而 pretty 和 fairly 通常不能这样用。

  The test results were somewhat better than we had expected.

  考试成绩比我们预期的稍好一些。

• fairly 本词

  Neutral in register, common in both speech and writing; weaker than pretty and used before plain adjectives rather than comparatives.

  语域中性，口语和书面语都常用；程度比 pretty 弱，通常放在普通形容词前，而不是比较级前。

  The hotel room was fairly small, but it was clean and quiet.

  这间酒店房间相当小，但是干净又安静。

Pretty, somewhat, and fairly all show a moderate degree. Pretty is informal and spoken, too casual for formal writing. Somewhat is more formal and written, often before comparatives like 'somewhat better'. Fairly is neutral, common in speech and writing, used before plain adjectives.

这三个词都用来表示程度，比“很”弱，但语域和搭配不同：pretty 偏口语、语气较强，fairly 语域中性、强度居中，somewhat 偏书面、常与比较级连用。这里不比较 pretty 作形容词“漂亮的”的用法。