Complaint made by a tiresome person (4,2,3,4)
I believe the answer is:
pain in the neck
'complaint' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'a tiresome person' is the wordplay.
I cannot really understand how this works, but
'a' is present in the answer.
'person' could be 'pi' (PI is an example) and 'pi' is located in the remaining letters.
This explanation may well be incorrect...
'made by' is the link.
Can you help me to learn more?
(Other definitions for pain in the neck that I've seen before include "Troublesome person or thing" , "Annoyance (colloq.)" , "bind" , "Very tiresome person or thing" , "Torticollis" .)