Decorating (8)
'decorating' is the definition.
('adorn' can be a synonym of 'decorate')
This is the entire clue.
(Other definitions for adorning that I've seen before include "Decorating with ornaments" , "Decorating, embellishing" , "decking" .)
(Other definitions for haste that I've seen before include "Expedition" , "make speed" , "go at speed" , "''More . . . . ., less speed'' (5)" , "Urgency of action" .)