A wave depresser (6)
I believe the answer is:
roller
'a wave' is the definition.
(I know that roller is a type of wave)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(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" .)