The most common and most likely answer to this crossword clue is the 10 letter word COUNTRYMAN
I've seen this crossword clue in The Guardian
C
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More clues leading to the result COUNTRYMAN
Buddy explains!

The straight part
We know that "fellow citizen" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fellow citizen = countryman.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 COUNTRYMAN mean?
COUNTRYMAN noun- Somebody from a certain country.
- Somebody from one's own country; a fellow countryman; compatriot.
- A country dweller, especially a follower of country pursuits.
- (traveller) A settled person, as opposed to a traveller.