The most common and most likely answer to this crossword clue is the 8 letter word DILIGENT
I've seen this crossword clue in The Guardian
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More clues leading to the result DILIGENT
- Tipping hat, one overseeing man, hard-working
- Reversing cap, one polite chap is hard-working
- Hard-working inspector, given illumination, taking information in
- Painstaking cover-up — it protects dope
- Conscientious editing changed round novel’s ending
- Painstaking policeman, liberal, a fine fellow
- Little woman left with one man should be careful
- Tipping hat, single man is assiduous
- Studious learner involved in editing novel
- Being thorough, get in after cover-up
Buddy explains!

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 DILIGENT mean?
DILIGENT adjective- Performing with industrious concentration; hard-working and focused.