Ritual involving one miracle (10)
I believe the answer is:
ceremonial
'ritual' is the definition.
(thesaurus)
'involving one miracle' is the wordplay.
'involving' indicates an anagram.
'one'+'miracle'='onemiracle'
'onemiracle' anagrammed gives 'CEREMONIAL'.
(Other definitions for ceremonial that I've seen before include "Ritual(istic)" , "Purely formal" , "Official" , "Ritual procedure" .)