He catches fish before eating one that's skinned (4)
I believe the answer is:
erne
'he catches fish' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'before eating one that's skinned' is the wordplay.
'before' becomes 'ere' (poetic term for 'before').
'eating' means one lot of letters goes inside another.
'that's skinned' means to look at the middle letters.
The middle letter of 'one' is 'n'.
'ere' enclosing 'n' is 'ERNE'.
Can you help me to learn more?
(Other definitions for erne that I've seen before include "Light (a flame)" , "Irish lough" , "Irish river, loughs; sea bird" , "Island-studded lake in Fermanagh" , "European sea eagle" .)