Do business (4)
'do business' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for operate that I've seen before include "Work - perform surgery" , "Conduct business in a theatre" , "Control, run, a machine say" , "Cut - run" , "Carry on business" .)
'business?' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'do' is the wordplay.
I cannot quite understand how this works, but
'do' could be 'ut' (synonyms) and 'ut' is present in the answer.
This explanation may well be incorrect...
(Other definitions for beauty parlour that I've seen before include "Grooming salon" , "Establishment for prettification" .)
'do business' is the definition.
(as in dealing with another business)
This is all the clue.
(Other definitions for deal that I've seen before include "Distribute playing cards" , "Sawn wood" , "split deck" , "Put cards on table" , "Timber - trade" .)