Opposite of rude (6)
I believe the answer is:
polite
'opposite of rude' is the definition.
('polite' is the opposite to 'rude')
This is the entire clue.
(Other definitions for polite that I've seen before include "Respectful and considerate" , "Mannerly, courteous" , "Minding one's p's and q's" , "Cultivated" , "(Of society) refined" .)