(used with verbs like[be, have,]and[do,]and with modal verbs, to express the opposite of the main verb, and also to express denial, refusal, prohibiting, etc.:I do not remember the answer. You must not think about it. It's not far from here. They are not coming.
(used with verbs like[think, want, seem, appear, expect,]and others that have another verb in a phrase or clause following, to express the opposite of the verb that follows):He did not seem to be ready (= It did not seem that he was ready). He did not want to go (= He wanted not to go.) I did not expect to see you here (= I expected that I wouldn't see you here).
(used before a singular count noun) not even one (expressing emphasis about the lack of something):[~ + a/one + noun]He had not a penny to his name. Not a single missile got through the defense system. Not one student could name the president.
Idioms
not at all:
(used as an answer to someone else's thanks):"I appreciate your help.'' —"Not at all.''
(used to emphasize an answer of "no''):"Did you like the show?'' —"Not at all!''