Crossword Genius

A drilling site (6,6)

Ross

I believe the answer is:

parade ground

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This clue might be a double definition.

'a drilling' is the first definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.

'site' is the second definition.
(thesaurus)

Can you help me to learn more?

(Other definitions for parade ground that I've seen before include "square" , "where there may be a muster" , "Place for drill" , "Where troops muster" , "Military area" .)

I've seen this clue in The Globe and Mail.
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