Britannica Dictionary definition of NOT
1
a
—
used to form the negative of modal verbs (such as “should” and “could”) and auxiliary verbs (such as “do” and “have”)
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He would/could not stay.
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We have not spoken with them.
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It may not be fast, but it's reliable.
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That kind of behavior should not be allowed.
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He did not seem to care.
b
—
used before a verb or clause to make it negative or give it an opposite meaning
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They gave us the option of not attending.
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She told me not to do it.
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You are not to go there without permission.
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He seemed not to care.
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It's odd, but that's not to say [=that does not mean] that it's bad.
—
see also not to mention at 1mention
2
a
—
used with a word or phrase to make it negative or give it an opposite meaning
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The books are not here.
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No, that's not what I said.
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That's not funny!
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That is not necessarily true.
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You're not always right.
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You are not the only one who is worried.
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She is not (at all/very) pleased/happy.
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I'm not happy or sad, just bored.
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It is not as easy as it seems.
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Things are not going well.
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He is not guilty.
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He lives not far from here.
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“Are we there yet?” “Not quite.”
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“Is there any left?” “Not much.”
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It is not just/only/merely [=more than just] a novel; it is a literary classic.
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Not many [=few] people showed up.
—
see also not a few at 1few
b
—
used with a negative word to make a positive statement
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Their request is not unreasonable. [=their request is reasonable]
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His experience is not unusual. [=others have had similar experiences]
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“What do you think of the food?” “It's not bad.” [=it's pretty good]
c
informal + humorous
—
used humorously at the end of a positive statement to show that you really meant the opposite
3
:
less or fewer than
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He was standing not six feet away from me.
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The bullet passed not five inches from my head!
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Not all of us agree. [=some of us do not agree]
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Not everybody finds her work interesting. [=some people find her work boring]
4
—
used to refer to a possible situation, condition, etc., that is different from or opposite to another situation, condition, etc.
—
often used in the phrase or not
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Believe it or not [=whether you believe me or don't believe me], we were there just last week.
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Ready or not, here I come!
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Like it or not, you'll do as he says. [=you'll do as he says whether you like or don't like it]
5
—
used to give a negative answer to a question
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“Do you think they forgot?” “I hope not.”
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“Should we go?” “I'd rather not.”
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“Do you think it's true?” “Probably/Certainly not.”
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“Do you mind?” “Not at all.”
as like as not
or
like as not
—
see 6like
more often than not
:
happening more than half the time
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He wins more often than not. [=he wins more than he loses]
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More often than not, I stay home instead of going out.
not a/one
:
no thing or person
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There was not one available taxi to be found. [=no taxis were available]
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Not a/one single person showed up. [=no one showed up]
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Not a word came out of her mouth.
not that
—
used to say that something said before is not important
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I tried to help, not that it mattered. [=but it did not matter]
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I saw him with some other woman, not that I care. [=but I don't care]