The most common and most likely answer to this crossword clue is the 7 letter word NEITHER
I've seen this crossword clue in The Daily Telegraph
N
E
I
T
H
E
R
More clues leading to the result NEITHER
- One squeezing bottom? On the contrary – not at all!
- In no case loose the rein
- First of injections in bottom? Not at all!
- One going in lower, not both
- Not one of two or three in disorder
- Doctor in there implying both options are ruled out
- First of injections in bottom? Not one thing or the other!
- I will cut inferior? Not at all
- In Brunei, the regime is not one thing nor the other
- No more iodine under boxes
Buddy explains!

The straight part
We know that "Not at all" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case not at all = neither.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 NEITHER mean?
NEITHER adverb- Similarly not.
- Not either one of two.
- Not either (used with nor).