seldom

Compared meaning: not happening often (adverb).

比较义项：很少、不常发生（副词）。

• rarely

  More common and neutral in everyday speech; used freely in both spoken and written English; often pairs with 'if ever'.

  更常见、语气中性，口语和书面语中都常用；常与“if ever”搭配。

  She rarely eats fast food because she prefers home cooking.

  她很少吃快餐，因为她更喜欢家常菜。

• seldom 本词

  More formal and literary; less common in casual conversation; can be fronted for emphasis, e.g. 'Seldom have I seen such skill.'

  语气更正式、偏书面，日常口语中较少使用；可以放在句首以示强调，如“Seldom have I seen such skill.”。

  He seldom eats breakfast before going to work in the morning.

  他早上上班前很少吃早餐。

Rarely and seldom both mean something happens very infrequently. Rarely is more common and neutral, used in both speech and writing. Seldom is more formal and literary, less common in casual talk, and can start a sentence for emphasis.

这两个词都表示某事发生的频率很低，可以互换用于大多数日常语境，但 seldom 语气更正式、略显书面，日常口语中较少使用；rarely 更常见、更中性，口语和书面语都常用。