About to include it in the ceremony (4)
I believe the answer is:
rite
'the ceremony' is the definition.
(rite is a kind of ceremony)
'about to include it' is the wordplay.
'about' becomes 're' ('re' means regarding or about).
'to include' means one lot of letters goes inside another.
're' placed around 'it' is 'RITE'.
'in' is the link.
(Other definitions for rite that I've seen before include "Formal procedure" , "form of service" , "Customary observance" , "Religious ceremonial sounds correct" , "Mystery - ceremony" .)