He attends to the top dressing (6)
I believe the answer is:
barber
'he attends to the top dressing' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'he attends to the top dressing' is the wordplay.
'he' becomes 'Bar'.
'attends' means one lot of letters go next to another.
'to the top dressing' becomes 'ber' (I can't justify this - if you can you should give a lot more credence to this answer).
'bar'+'ber'='BARBER'
Can you help me to learn more?
(Other definitions for barber that I've seen before include "Coiffeur" , "Hair stylist" , "who performs on the fringe?" , "A gent's haircutter" , "producing various versions of Hair?" .)