Sizeable order (4)
I believe the answer is:
tidy
I believe this clue is a double definition.
'sizeable' is the first definition.
('tidy' can be a synonym of 'sizeable')
'order' is the second definition.
(tidying is a kind of ordering)
(Other definitions for tidy that I've seen before include "Neaten" , "In good order" , "Neat - container for odds and ends" , "Spruce up" , "Systematic; substantial" .)