Barbershop powder (4)
I believe the answer is:
talc
'barbershop powder' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for talc that I've seen before include "Powdered substance" , "Powder used as toiletry" , "I may dust" , "Soft white powder" , "Bathroom dusting powder" .)