GI truly sorry in ceremony (7)
I believe the answer is:
liturgy
'ceremony' is the definition.
(liturgy is a kind of ceremony)
'gi truly sorry' is the wordplay.
'sorry' indicates an anagram (sorry can mean poor-quality or wretched).
'gi'+'truly'='gitruly'
'gitruly' anagrammed gives 'LITURGY'.
'in' is the link.
(Other definitions for liturgy that I've seen before include "ritual" , "Form of worship" , "Standard form of church service" , "church office" , "Prescribed forms for church services" .)