The most common and most likely answer to this crossword clue is the 10 letter word BOOTLEGGER
I've seen this crossword clue in The Daily Telegraph
B
O
O
T
L
E
G
G
E
R
More clues leading to the result BOOTLEGGER
Buddy explains!
The straight part
We know that "One operating still as a pirate" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one operating still as a pirate = bootlegger.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 BOOTLEGGER mean?
BOOTLEGGER noun- An illegal trader of goods, especially of alcohol.