The most common and most likely answer to this crossword clue is the 7 letter word ABETTER
I've seen this crossword clue in The Times
A
B
E
T
T
E
R
More clues leading to the result ABETTER
- Supporter in a cap
- A punter or a pimp?
- Criminal assistant one to have flutter?
- A superior partner in crime?
- A more desirable accessory
- Drink hosts dry in pursuit of a partner!
- Adult with superior accessory
- One more 25; he helps you in trouble
- An accomplice of a higher quality
- One who incites abstainer to crack a drink
Buddy explains!

The straight part
We know that "accessory" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case accessory = abetter.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 ABETTER mean?
ABETTER noun- One that abets an offender; one that incites; instigates; encourages.
- A supporter or advocate.