English theologian introducing a collection of old Norse poems (4)
I believe the answer is:
edda
'collection of old norse poems' is the definition.
'english theologian introducing a' is the wordplay.
'english' becomes 'e' (abbreviation).
'theologian' becomes 'dd' (Doctor of Divinity degree).
'introducing' is a charade indicator (letters next to each other).
'e'+'dd'+'a'='EDDA'
(Other definitions for edda that I've seen before include "Old Scandinavian book of poetry, etc" , "mythic florilegia" , "of Old Norse poems" , "Norse story" , "Old Icelandic book" .)