A harsh-sounding regimen (6)
I believe the answer is:
course
'regimen' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'a harsh-sounding' is the wordplay.
'a harsh' becomes 'coarse' (I've seen this in another clue).
'sounding' shows a homophone (sound like).
'coarse' sounds like 'COURSE'.
Can you help me to learn more?
(Other definitions for course that I've seen before include "Route along which something travels" , "Mode, of action say" , "way" , "Part of a meal (par for this?)" , "Curriculum" .)