Crossword Genius

History involving military's original retreat (9)

Ross

I believe the answer is:

hermitage

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'retreat' is the definition.
(I've seen this before)

I can't explain the remainder of the clue.

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(Other definitions for hermitage that I've seen before include "Recluse's abode" , "Museum housing collection started by Catherine the Great" , "accommodation for one" , "St Petersburg museum - Rhone wine" , "Place of retreat" .)

I've seen this clue in The Telegraph.
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