Shorten dress (4)
I believe the answer is:
trim
This clue is a double definition.
'shorten' is the first definition.
(thesaurus)
'dress' is the second definition.
('trim' can be a synonym of 'dress')
(Other definitions for trim that I've seen before include "Cut, prune; decorate" , "Neaten by cutting" , "Edging material - in good order" , "Make neat and smooth by cutting, say hair" , "Clip into shape" .)