Repair men do nothing less (4)
I believe the answer is:
mend
'repair' is the definition.
('mend' can be a synonym of 'repair')
'men do nothing less' is the wordplay.
'nothing' becomes 'o' (looks like zero - 0).
'less' suggests deleting specific letters.
'do' with 'o' removed is 'd'.
'men'+'d'='MEND'
(Other definitions for mend that I've seen before include "'Restore, fix (4)'" , "Heal" , "Return to health; repair" , "Put right" , "Make improvements" .)