With a fast speed, beat (4)
I believe the answer is:
lick
'beat' is the definition.
(synonyms)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for lick that I've seen before include "Lap; beat soundly" , "Taste" , "Lap; defeat" , "Personally clean" , "Lap -- beat hollow" .)