Crossword Genius

Beer voucher turned over (4)

Ross

I believe the answer is:

pils

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'beer' is the definition.
(Pilsner beer)

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for pils that I've seen before include "Lager beer" , "Type of lager" .)

I've seen this clue in The Times.
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