Beginning to slump, finish spoof (4-2)
I believe the answer is:
send-up
'spoof' is the definition.
(I know that spoof can be written as send-up)
'beginning to slump finish' is the wordplay.
'beginning to' says to take the initial letters.
'finish' becomes 'end up' (synonyms).
The initial letter of 'slump' is 's'.
's'+'endup'='SEND-UP'
(Other definitions for send-up that I've seen before include "Mockery" , "Spoof - jail" , "Parody" .)