Dispatch, say, about 50 (4)
I believe the answer is:
slay
'dispatch' is the definition.
('slay' can be a synonym of 'dispatch')
'say about 50' is the wordplay.
'about' is an insertion indicator.
'50' becomes 'l' (roman numeral).
'say' going around 'l' is 'SLAY'.
(Other definitions for slay that I've seen before include "Kill with premeditation" , "Kill, murder" , "Massacre" , "Violently kill" , "Fatally hit" .)