Peremptory request (6)
I believe the answer is:
demand
'peremptory request' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for demand that I've seen before include "Request forcefully" , "Ask peremptorily or call for" , "Claim; insist on" , "Request made emphatically as by right" , "Urgent or peremptory request" .)