Part of vital chalky drying agent (4)
I believe the answer is:
talc
'agent' is the definition.
The answer and definition can be both substances as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'part of vital chalky drying' is the wordplay.
'part of' indicates a hidden word.
'TALC' is hidden within 'vital chalky drying'.
Can you help me to learn more?
(Other definitions for talc that I've seen before include "After-bath powder" , "Magnesium silicate powder" , "Bathroom powder (abbr)" , "It is used to absorb moisture" , "Powdered mineral" .)