Arcane ceremony involves topless runner-up (9)
I believe the answer is:
recondite
'arcane' is the definition.
(thesaurus)
'ceremony involves topless runner-up' is the wordplay.
'ceremony' becomes 'rite' (rite is a kind of ceremony).
'involves' means one lot of letters goes inside another.
'topless' means to remove the first letter.
'runner-up' becomes 'second' (I've seen this before).
'second' with its initial letter taken off is 'econd'.
'rite' placed around 'econd' is 'RECONDITE'.
(Other definitions for recondite that I've seen before include "Abstruse" , "Mysterious" , "Difficult to understand" , "not widely known" , "(Of knowledge) obscure" .)