Englishfor English speakers
the
Determiner
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Used, instead of a, to reference something specific, already known to exist.
Compare "I read a book." and "I read the book."
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Used with a stress, to show that the word following is special.
Are you the John Smith that I went to school with?
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Used with an adjective that acts like a noun to mean all of the people concerned
The poor are always with us.
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Used with superlatives forms of adjectives and adverbs.
You are the best.
day
Noun
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A day is a measure of time.
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24 hours
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Seven days make one week
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The time between midnight and the following midnight (or between sunset and sunset in Jewish reckoning)
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The time between sunrise and sunset, when it is daylight
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The part of a day spent at work or school
He spent two days at work means that on two days he went to work; he did not spend 48 hours at work.