Refuse to go downhill (7)
I believe the answer is:
decline
I believe this is a triple definition!
'refuse' is the first definition.
(synonyms)
'to go' is the second definition.
(thesaurus)
'downhill' is the third definition.
(thesaurus)
(Other definitions for decline that I've seen before include "perform grammatical exercise" , "Diminution" , "Fade" , "Refuse to accept" , "Say no or lose strength" .)