Trump sounding coarse (5)
I believe the answer is:
rough
'coarse' is the definition.
(similar in meaning)
'trump sounding' is the wordplay.
'trump' becomes 'ruff' (synonyms).
'sounding' shows a homophone (sound like).
'ruff' sounds like 'ROUGH'.
(Other definitions for rough that I've seen before include "Delinquent" , "Hooligan - lacking refinement" , "Not smooth, even or regular" , "Unpolished" , "Hard - coarse - inexact" .)