I complain when the girl is upset (5)
I believe the answer is:
naomi
'upset' is the definition.
Both the definition and answer are singular nouns.
Perhaps you can see a link between them that I can't see?
'i complain when the girl' is the wordplay.
I cannot really see how this works, but
'i' could be 'a' and 'a' is found in the answer.
'girl' could be 'nomi' and 'nomi' is found in the leftover letters.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'is' acts as a link.
Can you help me to learn more?
(Other definitions for naomi that I've seen before include "Ruth's mother-in-law (Bible)" , "-- Campbell, British model" , "Girl" , "Do I moan about Biblical Ruth's mother-in-law?" , "Ruth's mother-in-law (Old Testament)" .)