Fish a theologian steeped in wine (7)
I believe the answer is:
haddock
'fish' is the definition.
(haddock is a kind of fish)
'a theologian steeped in wine' is the wordplay.
'theologian' becomes 'DD' (Doctor of Divinity degree).
'steeped in' means one lot of letters goes inside another (I've seen this in other clues).
'wine' becomes 'hock' (type of wine).
'a'+'dd'='add'
'add' going inside 'hock' is 'HADDOCK'.
(Other definitions for haddock that I've seen before include "Swimmer" , "ish" , "Fish, often smoked" , "Fish like cod but smaller" , "Fish similar to but smaller than cod" .)