Proper ceremony, say (5)
I believe the answer is:
right
'proper' is the definition.
(I know that proper can be written as right)
'ceremony say' is the wordplay.
'ceremony' becomes 'rite' (rite is a kind of ceremony).
'say' indicates a 'sounds like' (homophone) clue.
'rite' sounds like 'RIGHT'.
(Other definitions for right that I've seen before include "OK?" , "Not left" , "Privy Councillors are so honourable" , "Most favourable" , "Correct - starboard" .)