Criticise long dash (7)
I believe the answer is:
panache
'dash' is the definition.
('panache' can be a synonym of 'dash')
'criticise long' is the wordplay.
'criticise' becomes 'pan' (informal term meaning to criticise heavily).
'long' becomes 'ache' ('ache' can be a synonym of 'long').
'pan'+'ache'='PANACHE'
(Other definitions for panache that I've seen before include "Style, elan" , "Flamboyant confidence" , "Sense of style, swagger" , "Swagger; theatricality" , "A dashing manner" .)