daytime

Compared meaning: the time when it is light outside (noun).

比较义项：白天，天亮着的时间（名词）。

• day

  The most common, general word for the light part of a 24-hour period; used in everyday phrases like 'during the day'; also has an unrelated sense (a calendar date), not compared here.

  最常见、最口语化的说法，指一天中天亮的部分，常用于“during the day”这类日常表达；day 还有“日期／哪一天”的意思，此处不比较。

  The days are getting longer now that spring has arrived.

  既然春天已经到了，白天正变得越来越长。

• daytime 本词

  A slightly more formal, technical noun for the period of light in a day, often contrasted with 'nighttime' and common in weather, schedule or broadcast contexts.

  语气稍正式、偏专业的名词，指一天中天亮的时段，常与“nighttime（夜间）”相对，多见于天气、日程、电视节目等语境。

  Daytime temperatures in the desert can exceed forty degrees.

  沙漠地区白天的气温可能超过四十度。

• daylight

  Refers to the natural light itself rather than the time period; used in fixed phrases like 'in broad daylight' or 'before daylight', or when talking about how much light is available.

  指白天的自然光线本身，而不是指时间段；常用于“in broad daylight（光天化日之下）”“before daylight（天亮之前）”等固定说法，或用来说明光线是否充足。

  Turn off the lamp — there's still enough daylight to read by.

  把台灯关掉吧——现在天还亮着，自然光足够看书了。

All three can mean the time it is light outside. Day is the most common word; it also means a calendar date, not compared here. Daytime is a formal noun, contrasted with 'nighttime'. Daylight refers to the light itself, not the time period.

day、daytime、daylight 在这个义项上都指“天亮的时候”，但侧重点不同：day 最常用、最口语化，daytime 更强调与夜晚相对的一段时间，daylight 强调的是光线本身而不是时间段。这里不比较 day 表示“一天／日期”的其他义项（如 What day is it?）。