One's car could become rougher (7)
I believe the answer is:
coarsen
'one's car could become rougher' is the definition.
I can't tell whether this defines the answer.
'one's car could become' is the wordplay.
'could become' indicates an anagram.
'ones'+'car'='onescar'
'onescar' with letters rearranged gives 'COARSEN'.
Can you help me to learn more?
(Other definitions for coarsen that I've seen before include "become inferior" , "Dull" , "Make more harsh" , "Make rougher" , "Turn rough" .)