Part essential to care arrangements (4)
I believe the answer is:
area
'part' is the definition.
(area is a kind of part)
'essential to care arrangements' is the wordplay.
'essential to' indicates the answer is hidden within the clue (I've seen this in other clues).
'AREA' is hidden in the letters of 'care arrangements'.
(Other definitions for area that I've seen before include "Geographical region" , "The measure of a surface" , "land" , "Extent of a 2-dimensional surface" , "Expanse of a surface" .)