The most common and most likely answer to this crossword clue is the 12 letter word INVESTIGATOR
I've seen this crossword clue in The Times
I
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V
E
S
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More clues leading to the result INVESTIGATOR
- Wearing garment with one gun, soldiers who may be on the prowl?
- Ringleader taking in very English sleuth
- Explorer, perhaps, wearing singlet — one meeting reptile
- Detective wearing very little confronting dangerous creature on island
- Detective with unsteady gait held by one with money to place
- Detective wearing singlet on air got rattled
Buddy explains!

The straight part
We know that "sleuth" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sleuth = investigator.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 INVESTIGATOR mean?
INVESTIGATOR noun- One who investigates.