Question remains after defeat (5)
I believe the answer is:
quash
'defeat' is the definition.
(quash can mean to defeat or suppress)
'question remains after' is the wordplay.
'question' becomes 'qu' (abbreviation).
'remains' becomes 'ash' (remains of a fire).
'after' says to put letters next to each other.
'qu'+'ash'='QUASH'
(Other definitions for quash that I've seen before include "Subdue" , "Invalidate" , "Suppress or crush, say a rebellion" , "Put down" , "Suppress -- annul" .)