Defeats terrible beast (5)
I believe the answer is:
beats
'defeats' is the definition.
(beating is a kind of defeating)
'terrible beast' is the wordplay.
'terrible' is an anagram indicator.
'beast' with letters rearranged gives 'BEATS'.
(Other definitions for beats that I've seen before include "Buffets" , "Tans" , "Rhythms" , "Regular routes for policemen" .)