Drier used in hospital constantly (4)
I believe the answer is:
talc
'drier' is the definition.
(I've seen this before)
'in hospital constantly' is the wordplay.
'in' indicates the answer is hidden within the clue.
'TALC' is hidden within 'hospital constantly'.
'used' is the link.
(Other definitions for talc that I've seen before include "I may dust" , "Toilet powder - mica" , "Baby powder" , "Powdered mineral" , "(Mineral providing) powder" .)