Waves from posh cars, commonly (7)
I believe the answer is:
rollers
I believe this clue is a double definition.
'waves' is the first definition.
(roller is a kind of wave)
'posh cars commonly' is the second definition.
(informal name for Rolls Royces)
'from' acts as a link.
(Other definitions for rollers that I've seen before include "expensive cars" , "Long heavy sea waves" , "They may be used to paint" .)