Work's endless for boss (4)
I believe the answer is:
stud
'for boss' is the definition.
('stud' can be a synonym of 'boss')
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for stud that I've seen before include "Football boot attachment" , "Bolt" , "Removable collar button" , "Animal breeding farm" , "Part of a football boot" .)