The most common and most likely answer to this crossword clue is the 3 letter word NOR
I've seen this crossword clue in The Times
N
O
R
More clues leading to the result NOR
- …and not nervous of retirement at first
- Negative word embraced by politician, ordinarily
- Joiner, Pole, taking Thursday off
- … and not half common!
- ... and not what’s expected, not quite
- Half-past ten? Ridiculous, we snort
- In addition, not taking mark off standard
- Neither of half-cut dons nursed regrets at first
- Get neither number right
- It helps to show direction
Buddy explains!

The straight part
We know that "and not" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case and not = nor.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does NOR mean?
NOR conjunction- And not (introducing a negative statement, without necessarily following one).
- A function word introducing each except the first term or series, indicating none of them is true.
- Used to introduce a further negative statement.
- Than.
- A binary operator composite of NOT OR; negation of OR function.
- Acronym of nucleolus organiser region.