Half-hearted floor cleaner is a misery (5)
I believe the answer is:
moper
'misery' is the definition.
Both the definition and answer are singular nouns.
Maybe there's an association between them I don't understand?
'half-hearted floor cleaner is a' is the wordplay.
'half hearted floor cleaner' becomes 'mo' (I can't explain this - if you can you should give a lot more credence to this answer).
'is a' becomes 'per' (eg 'one a day' means 'one per day').
'mo'+'per'='MOPER'
Can you help me to learn more?
(Other definitions for moper that I've seen before include "Weary Willie" , "One who's depressed" .)