The most common and most likely answer to this crossword clue is the 5 letter word SEPOY
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More clues leading to the result SEPOY
Buddy explains!

The straight part
We know that "Foreign soldier" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case foreign soldier = sepoy.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 SEPOY mean?
SEPOY noun- A native soldier of the East Indies, employed in the service of a European colonial power, notably the British India army (first under the British-chartered East India Company, later in the crown colony), but also France and Portugal.