A wave depresser (6)

I believe the answer is:

roller

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'a wave' is the definition.
(I know that roller is a type of wave)

I cannot understand how the rest of the clue works.

(Other definitions for roller that I've seen before include "Kind of skate" , "Wave; castor; cylinder" , "Cylinder for flattening etc" , "One may be employed to paint" , "flattens lawn" .)

I've seen this clue in The Irish News.

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