Meaning of “not” - Learner’s Dictionary

not

adverb uk us /nɒt/

A1 used to form a negative phrase after verbs like 'be', 'can', 'have', 'will', 'must', etc, usually used in the short form 'n't' in speech:

I won't tell her.
I can't go.
He hasn't eaten yet.
Don't you like her?
It isn't difficult (= It is easy).
The service isn't very good (= it is bad).
You're coming, aren't you?
I will not tolerate laziness.

A1 used to give the next word or group of words a negative meaning:

I told you not to do that.
I like most vegetables but not cabbage.
"Come and play football, Dad." "Not now, Jamie."
"Whose are these?" "Not mine."

A2 used after verbs like 'be afraid', 'hope', 'suspect', etc in short, negative replies:

"Do you think it's going to rain?" "I hope not."
"Have you finished?" "I'm afraid not."
certainly/hopefully not

used after an adverb in short, negative replies:

"She's not exactly poor, is she?" "Certainly not."
"We won't need much money, will we?" "Hopefully not."
not at all

B2 used instead of 'no' or 'not' to emphasize what you are saying:

"I hope this won't cause you any trouble." "No, not at all."
I'm not at all happy about it.
Not at all.

B1 used as a polite reply after someone has thanked you:

"Thanks for all your help." "Not at all."
if not

A2 used to say what the situation will be if something does not happen:

I hope to see you there but, if not, I'll call you.
or not

A2 used to express the possibility that something might not happen:

Are you coming or not?
not a/one

used to emphasize that there is nothing of what you are talking about:

Not one person came to hear him talk.
"You haven't heard from Nick, have you?" "Not a word."

(Definition of “not” from the Cambridge Learner’s Dictionary © Cambridge University Press)