Englishfor English speakers
certain
Adjective
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If you are certain of something, you believe it to be true without doubt.
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If something is certain, it will happen without doubt.
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If you make certain of something, you check that it is true or correct.
certain
Determiner
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Used to talk about groups or individuals without saying exactly which one(s).
Certain problems can be solved with very simple math.
Her job gave her a certain freedom.
Certain of the members did not agree.
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.