ad.

1. 不
   He is not a member of the Union.

   他不是工会会员。

2. （用来代替并否定一个词组或句子）不，不会
   Drop that gun! If not, you'll be sorry.

   把枪扔下！否则你会后悔的。

3. （与否定词一起构成双重否定表肯定）并非，不怎么
   They refused her request not without good reason.

   他们不无道理地拒绝了她的请求。

4. （与all, both, every连用表示部分否定）不都是，不全是
   Both houses are not white.

   两所房子不都是白色的。

adv.

1. (also n't joined to a preceding verb) used chiefly with an auxiliary verb or ‘be’ to form the negative.
2. used as a short substitute for a negative clause.
3. used to express the negative of other words.
   ▸used with a quantifier to exclude a person or part of a group.
   ▸less than.
4. used in understatements to suggest that the opposite of a following word or phrase is true:
   not a million miles away.
   ▸informal, humorous following and emphatically negating a statement:

   that sounds like quality entertainment—not!

n.

1. a logical operation which gives the value zero if the operand is one, and vice versa.
2. [as modifier] Electronics  denoting a gate circuit which produces an output only when there is no input signal.