What does day mean?
Day is one of the most fundamental nouns in English, denoting a period of twenty-four hours measured from one midnight to the next. It also refers more narrowly to the portion of that period when daylight is present, in contrast to night. Beyond these literal senses, day extends to specific calendar dates ('her birthday is an important day'), to eras or lifetimes ('in his day, travel was slower'), and to commemorated occasions such as holidays and observances. The word appears constantly in everyday idiom — people work 'day after day', make decisions 'at the end of the day', and stop labouring when they 'call it a day'. Its derivatives, including daily, daylight, daytime, and daybreak, show how deeply it is woven into how English speakers structure time. Simple, ancient, and indispensable, day remains among the most frequently used words in the language.
nounA period of twenty-four hours, especially as a unit of time reckoned from one midnight to the next. Also the part of this period during which daylight is present, as opposed to night.
- A period of twenty-four hours reckoned from one midnight to the next.
- The period of natural light between dawn and dusk; the time when it is not dark.
- A particular date on the calendar.
- (figurative) A person's lifetime or era of prominence; one's prime.
- A day designated for a specific purpose (e.g. Independence Day).
"She spent the whole day working on her thesis."
"It was a bright, clear day, perfect for a walk along the coast."
"In her day, women were rarely admitted to medical school."
Standard plural. In idiomatic expressions such as 'in those days' or 'days gone by', the plural often refers to a general historical period rather than a counted number of individual days.
"Those were the days when we would spend summers at the lake."
Before mechanical clocks, 'day' could mean the full 24 hours — or just the daylight portion — which is why phrases like 'the day is long' once meant something subtly different.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of day
Day comes from Old English dæg, meaning the period between sunrise and sunset or a full rotation of the earth. It shares ancestry with related Germanic forms such as Old Saxon dag, Old High German tag, and Gothic dags. Cognate words include dial and diary through their Latin root diēs (meaning day), though diēs itself is not directly cognate with the Germanic form.
Related word forms
How day is actually used
Common in all registers from casual to formal. In idiomatic use, 'day' often carries figurative weight ('end of the day', 'one's day') that goes well beyond its literal temporal meaning.
Easily confused with day
'Daze' means a stunned or confused mental state and rhymes with 'day', whereas 'day' refers to the twenty-four-hour period.