The most common and most likely answer to this crossword clue is the 6 letter word USABLE
I've seen this crossword clue in The Times
U
S
A
B
L
E
More clues leading to the result USABLE
- Posh fur fit for purpose
- Working uniform, black
- Working American president touring capital of Louisiana
- Black under uniform is functional
- Book set in university town in Cheshire is fit for purpose
- Working with American on island, heading west
- Posh fur can be exploited
- Ready for service, nuns gambolled every now and then
- A blues composition, fit for purpose
- Upper-class fur ready-to-wear?
Buddy explains!

The straight part
We know that "fit for purpose" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fit for purpose = usable.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 USABLE mean?
USABLE adjective- Capable of being used.
- Easy to use; exhibiting good usability.
- Homosexual