The day before getting new uniform (4)
I believe the answer is:
even
'uniform' is the definition.
(uniform can mean even or level)
'the day before getting new' is the wordplay.
'the day' becomes 'eve' (eve is a kind of day).
'before getting' says to put letters next to each other.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'eve'+'n'='EVEN'
(Other definitions for even that I've seen before include "end of the day, reading poetry" , "Like 2,4,6, ..." , "night" , "of consistent quality" , "Still - flat" .)