Unpleasant ride a beagle’s suffering (12)
I believe the answer is:
disagreeable
'unpleasant' is the definition.
(synonyms)
'ride a beagle's suffering' is the wordplay.
'suffering' indicates anagramming the letters.
'ride'+'a'+'beagles'='rideabeagles'
'rideabeagles' anagrammed gives 'DISAGREEABLE'.
(Other definitions for disagreeable that I've seen before include "Offensive - peevish" , "Unpleasant" , "Bad-tempered" , "Obnoxious" .)