College ceremony ends early for one key judge (6)
I believe the answer is:
critic
'judge' is the definition.
(critic is a kind of judge)
'college ceremony ends early for one key' is the wordplay.
'college' becomes 'c'.
'ceremony' becomes 'rite' (rite is a kind of ceremony).
'ends early' means to remove the last letter (I've seen 'ending early' mean this).
'for' is a charade indicator (letters next to each other).
'one key' becomes 'ic' (I can't justify this - if you can you should give a lot more credence to this answer).
'rite' with its final letter taken off is 'rit'.
'c'+'rit'+'ic'='CRITIC'
Can you help me to learn more?
(Other definitions for critic that I've seen before include "Reviewer of book or play" , "Newspaper reviewer" , "Professional reviewer of literature, art, drama or music" , "Professional judge" , "Writer of opinions on plays, concerts etc" .)