Fashion a new dome (4)
I believe the answer is:
mode
'fashion' is the definition.
('mode' can be a synonym of 'fashion')
'a new dome' is the wordplay.
'a new' is an anagram indicator.
'dome' with letters rearranged gives 'MODE'.
(Other definitions for mode that I've seen before include "Manner of dome" , "Style of dome" , "Style, method" , "Trend" , "Custom" .)