What a screen may be made of (5)

I believe the answer is:

smoke

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'what a screen' is the definition.
(smoke screen is a kind of screen)

I can't explain the rest of the clue.

(Other definitions for smoke that I've seen before include "Visible vapour" , "'There's no . . . . . without fire'" , "cause of a cough?" , "Fumigate; cigarette" , "Cure (food) - endanger health!" .)

I've seen this clue in the Evening Standard.

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