Tiresome job that's unhealthy (3)
I believe the answer is:
fag
'tiresome job' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps there's an association between them I don't understand?
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for fag that I've seen before include "Ciggie" , "smoke" , "Tedious chore" , "Boring task" , "He'll do anything you ask" .)