not

Concise Oxford English Dictionary © 2008 Oxford University Press:
not/nɒt/

▶adverb

• 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!

▶noun (NOT)

• 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.

– origin ME: contr. of nought.