Ecstatic about ace stuff in ceremony (9)
I believe the answer is:
sacrament
'ceremony' is the definition.
(sacrament is a kind of ceremony)
'ecstatic about ace stuff' is the wordplay.
'ecstatic' becomes 'sent' (I've seen this in other clues).
'about' is an insertion indicator.
'ace' becomes 'a'.
'stuff' becomes 'cram' (synonyms).
'a'+'cram'='acram'
'sent' placed around 'acram' is 'SACRAMENT'.
'in' acts as a link.
(Other definitions for sacrament that I've seen before include "Religious ceremony" , "Eucharist, for example" , "Religious ritual" , "Orders" , "A mystery of the church" .)