Disdain continued briefly, almost completely futile (8)
I believe the answer is:
contempt
'disdain' is the definition.
(synonyms)
'continued briefly almost completely futile' is the wordplay.
'continued briefly' becomes 'cont' (common abbreviation; 'briefly' asks for an abbreviation).
'almost completely' means to remove the last letter.
'futile' becomes 'empty'.
'empty' with its last letter taken off is 'empt'.
'cont'+'empt'='CONTEMPT'
(Other definitions for contempt that I've seen before include "Disregard for the rules of a court of law" , "Complete lack of respect, as sometimes of court" , "The feeling of despising a person" , "Disdain, say, perhaps of court" , "Feeling of despising something - perhaps court?" .)