The most common and most likely answer to this crossword clue is the 3 plus 2 letter word NOT ON
N
O
T
O
N
More clues leading to the result NOT ON
- Unacceptable idea I dismissed
- Unacceptable, whichever way you look at it
- Either way, it's unacceptable
- Impossible, raising leg weight
- Unfeasible going north or south
- Unsportsmanlike yo-yoing?
- Unacceptable idea I abandoned
- Out in the nineties, so this impossible!
- Idea lacking information? Either way it’s unacceptable
- Unacceptable to only score 99?
Buddy explains!

The straight part
We know that "Unacceptable" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case unacceptable = not on.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.