This part-song is clearly no dirge (4)
I believe the answer is:
glee
'clearly no dirge' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'this part-song' is the wordplay.
I cannot really see how this works, but
'part' could be 'lee' (lee is a kind of part) and 'lee' is located in the answer.
A single letter 'g' remains which might be clued in a way I don't understand.
This explanation may well be incorrect...
'is' is the link.
Can you help me to learn more?
(Other definitions for glee that I've seen before include "Great pleasure" , "Unholy mirth or triumphant joy" , "(Malicious) satisfaction" , "Mirth - part-song" , "Sort of club" .)