Dull fashion dies out (7)
I believe the answer is:
tedious
'dull' is the definition.
(I know that dull can be written as tedious)
'fashion dies out' is the wordplay.
'fashion' indicates anagramming the letters.
'dies'+'out'='diesout'
'diesout' with letters rearranged gives 'TEDIOUS'.
(Other definitions for tedious that I've seen before include "not exciting" , "Banal" , "Wearisome, boring" , "flat" , "Tiresome, boring" .)