Brusque retreat before English ceasefire (5)
I believe the answer is:
truce
'ceasefire' is the definition.
(I've seen this before)
'brusque retreat before english' is the wordplay.
'brusque' becomes 'curt' ('curt' can be a synonym of 'brusque').
'retreat' says the letters should be written in reverse.
'before' means one lot of letters go next to another.
'english' becomes 'e' (abbreviation).
'curt' backwards is 'truc'.
'truc'+'e'='TRUCE'
(Other definitions for truce that I've seen before include "Temporary halt in hostilities" , "peace initiative" , "Agreement to suspend fighting" , "Respite" , "bit of peace" .)