They have taken cover on hills (7)

I believe the answer is:

captors

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'they have taken' is the definition.
The definition suggests an adverb but the answer is not.

'cover on hills' is the wordplay.
'cover' becomes 'cap' (cap is a kind of cover).
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'hills' becomes 'tors' (tor is a kind of hill).
'cap'+'tors'='CAPTORS'

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

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