Raise flag (4)

I believe the answer is:

jack

I believe this is a double definition.

'raise' is the first definition.
(jacking is a kind of raising)

'flag' is the second definition.
(I know that jack is a type of flag)

(Other definitions for jack that I've seen before include "bowler rolls it" , "Man in navy" , "Device for raising car to remove wheel" , "Male donkey" , "Sailor; flag" .)

I've seen this clue in The Guardian, The Sunday Times and The Times.

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