Learner's 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”)不，没有（用于构成情态动词should、could及助动词do、have等的否定形式） -
He would/could not stay.他不会/不能留下来。
-
We have not spoken with them.我们还没有和他们交谈。
-
It may not be fast, but it's reliable.它可能速度不快，但是可靠。
-
That kind of behavior should not be allowed.不应该允许这种行为。
-
He did not seem to care.他似乎并不在乎。
b —
used before a verb or clause to make it negative or give it an opposite meaning不，不要（用在动词或从句前表示否定） -
They gave us the option of not attending.他们给我们的选择是不出席。
-
She told me not to do it.她告诉我别这样做。
-
You are not to go there without permission.未经允许你不许去那里。
-
He seemed not to care.他似乎并不在乎。
-
It's odd, but that's not to say [=that does not mean] that it's bad.这很古怪，但并不意味着不好。
— 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不，没有（与单词或短语连用表示否定） -
The books are not here.这些书不在这里。
-
No, that's not what I said.不，那不是我说的。
-
That's not funny!可不是闹着玩的！
-
That is not necessarily true.那未必是真的。
-
You're not always right.你并非总是对的。
-
You are not the only one who is worried.你不是唯一担心的人。
-
She is not (at all/very) pleased/happy.她（一点也/非常）不高兴/不开心。
-
I'm not happy or sad, just bored.我不高兴也不难过，只是无聊而已。
-
It is not as easy as it seems.事情似乎没有看上去那么简单。
-
Things are not going well.事情进展不顺利。
-
He is not guilty.他没有罪。
-
He lives not far from here.他住得离这儿不远。
-
“Are we there yet?” “Not quite.”“我们到了吗？”“还没有。”
-
“Is there any left?” “Not much.”“还有剩余的吗？”“不多了。”
-
It is not just/only/merely [=more than just] a novel; it is a literary classic.它不仅仅是一部小说，更是一部文学经典。
-
Not many [=few] people showed up.来的人不多。
— see also not a few at 1few b —
used with a negative word to make a positive statement与否定词连用表肯定 -
Their request is not unreasonable. [=their request is reasonable]他们的要求并非不合理。
-
His experience is not unusual. [=others have had similar experiences]他的经历没什么特别的。
-
“What do you think of the food?” “It's not bad.” [=it's pretty good]“你认为这食物怎么样？”“相当不错。”
c informal + humorous —
used humorously at the end of a positive statement to show that you really meant the opposite才怪（用在肯定陈述后，作诙谐用法） 3
: less or fewer than不到；少于 -
He was standing not six feet away from me.他在离我不到六英尺的地方站着。
-
The bullet passed not five inches from my head!子弹从距离我的头不到五英寸的地方飞过！
-
Not all of us agree. [=some of us do not agree]并非我们大家都同意！
-
Not everybody finds her work interesting. [=some people find her work boring]不是每个人都觉得她的作品有趣。
4
—
used to refer to a possible situation, condition, etc., that is different from or opposite to another situation, condition, etc.并非（用于指可能存在相反情况） —
often used in the phrase or not常用于短语or not -
Believe it or not [=whether you believe me or don't believe me], we were there just last week.不管你信还是不信，我们上周还在那儿呢。
-
Ready or not, here I come!不管是否准备好，我来了！
-
Like it or not, you'll do as he says. [=you'll do as he says whether you like or don't like it]不管你乐意还是不乐意，你得按他说的做。
5
—
used to give a negative answer to a question不，没有（用于否定回答） -
“Do you think they forgot?” “I hope not.”“你认为他们忘了吗？”“但愿没有。”
-
“Should we go?” “I'd rather not.”“我们可以走了吗？”“我不想走。”
-
“Do you think it's true?” “Probably/Certainly not.”“你认为那是真的吗？”“可能/肯定不是。”
-
“Do you mind?” “Not at all.”“你介意吗？”“不介意。”
as like as not
or like as not — see 6like
more often than not
: happening more than half the time多数时候；多半 -
He wins more often than not. [=he wins more than he loses]他赢的时候多。
-
More often than not, I stay home instead of going out.我多数时候并不出门，只待在家里。
not a/one
: no thing or person一个也没有 -
There was not one available taxi to be found. [=no taxis were available]一辆出租车也找不到。
-
Not a/one single person showed up. [=no one showed up]一个人也没有出现。
-
Not a word came out of her mouth.她一个字也没说。
not that
—
used to say that something said before is not important倒不是；并不是说 -
I tried to help, not that it mattered. [=but it did not matter]我尽量帮忙，但这不是什么大事。
-
I saw him with some other woman, not that I care. [=but I don't care]我看见他和别的女人在一起，但我并不介意。