Dress up, with "out" (3)
I believe the answer is:
tog
'dress up with out' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for tog that I've seen before include "Measure of warmth" , "Provide with clothes" , "Unit of thermal resistance, used for duvets" , "Garment" , "Duvet rating" .)