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