Defeat at a good speed (4)
I believe the answer is:
lick
This could be a double definition.
'defeat' is the first definition.
(lick can mean to beat or defeat)
'a good speed' is the second definition.
'lick' can be an answer for 'speed' (I've seen this before). I'm not sure about the 'a good' bit.
'at' is the link.
Can you help me to learn more?
(Other definitions for lick that I've seen before include "Jazz phrase" , "Feel with the tongue" , "compressed salt for domestic animals" , "Lap; trounce" , "Personally clean" .)