Dreadful sort of ride (4)
I believe the answer is:
dire
'dreadful' is the definition.
(synonyms)
'sort of ride' is the wordplay.
'sort of' indicates anagramming the letters.
'ride' anagrammed gives 'DIRE'.
(Other definitions for dire that I've seen before include "Really dreadful - ride on" , "Disastrous" , "Ominous; very bad" , "to speak (13) [FRENCH]" , "Ride in dreadful state" .)