Angelus, say in short form is capital (8)
I believe the answer is:
belgrade
'is capital' is the definition.
(I've seen this before)
'angelus say in short form' is the wordplay.
'angelus say' becomes 'bell' (angelus is a kind of bell).
'in short' means to remove the last letter.
'form' becomes 'grade' (synonyms).
'bell' with its last letter removed is 'bel'.
'bel'+'grade'='BELGRADE'
(Other definitions for belgrade that I've seen before include "Foreign capital" , "Balkan capital" , "Capital city - large bed (anag)" , "Serbian capital" , "In foreign city" .)