Sticks up for superior (4)
I believe the answer is:
smug
'for superior' is the definition.
(I've seen this before)
'sticks up' is the wordplay.
'sticks' becomes 'gums'.
'up' is a reversal indicator (in down clue: letters go upwards).
'gums' backwards is 'SMUG'.
(Other definitions for smug that I've seen before include "Spruce" , "Overly complacent" , "Irritatingly self-satisfied" , "goody-goody" , "Unctuous" .)