Source, we assume, of a fine piece of poetry (5)
I believe the answer is:
donne
'source' is the definition.
The answer and definition can be both people as well as being singular nouns.
Maybe you can see an association between them that I can't see?
'we assume of a fine piece of poetry' is the wordplay.
I cannot quite understand how this works, but
'assume' could be 'don' (I've seen this before) and 'don' is found in the answer.
'piece' could be 'n' (abbreviation for Knight in chess notation) and 'n' is present in the answer.
A single letter 'e' remains which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for donne that I've seen before include "John -, English poet" , "Writer of poetry" , "English preacher and metaphysical poet, d. 1631" , "basic assumption" .)