infrequent

Compared meaning: not happening often (adjective).

比较义项：偶尔发生、不经常（形容词）。

• occasional

  Describes something that happens now and then without a regular pattern, often with a light, casual tone, as in an occasional treat or visitor.

  描述某事不定期地偶尔发生，语气较为随意、轻松，例如“偶尔的款待”或“偶尔来访的客人”。

  He treats himself to an occasional slice of cake after dinner.

  他偶尔会在晚饭后犒劳自己一块蛋糕。

• infrequent 本词

  Describes something that happens rarely or at long intervals, used more objectively about frequency (e.g. transport, events), and sounds more formal, often implying inconvenience.

  描述某事很少发生或间隔很长时间才发生一次，多用于客观描述频率（如交通、活动），语气更正式，常带有不便的意味。

  Trains to this remote town are infrequent, sometimes only one a day.

  开往这个偏远小镇的火车班次很少，有时一天只有一趟。

Occasional and infrequent both mean something does not happen often. Occasional describes something happening now and then, with no regular pattern, in a light, casual tone. Infrequent describes something happening rarely, at long intervals, in a more formal way, often implying inconvenience.

这两个词都表示事情发生得不频繁，但语气不同：occasional 强调偶然、不规律，语气较随意甚至带轻松感；infrequent 强调发生频率低、少见，语气更正式客观，常带不便的意味。