Set on a particular course but utterly defeated (6)
I believe the answer is:
routed
'defeated' is the definition.
(similar in meaning)
'set on a particular course but utterly' is the wordplay.
I cannot quite see how this works, but
'course' could be 'route' (both can mean a path) and 'route' is found within the answer.
A single letter 'd' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for routed that I've seen before include "Sent (by a particular path)" , "Sent (along a specified course)" , "Put to flight or directed" , "getting beaten" , "Caused to flee" .)