Ceremony that's appropriate to be heard (4)
I believe the answer is:
rite
'ceremony' is the definition.
(rite is a kind of ceremony)
'appropriate to be heard' is the wordplay.
'appropriate' becomes 'right' ('right' can be similar in meaning to 'appropriate').
'to be heard' shows a homophone (sound like).
'right' sounds like 'RITE'.
'that's' is the link.
(Other definitions for rite that I've seen before include "Ceremony, liturgy" , "Custom" , "Tire of ceremony" , "Established religious ceremony" , "Mystery - ceremony" .)