Separate section (4)
This clue is a double definition.
'separate' is the first definition.
(both can mean to split or break apart)
'section' is the second definition.
(I know that section is a more specific form of the action part)
(Other definitions for part that I've seen before include "Bit - leave" , "Portion of a whole" , "Separate - role" , "Divide; role" , "unemployed actor hopes for" .)
'separate section' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for compartment that I've seen before include "Section of railway carriage etc" , "Division of rail carriage" , "cubicle" , "Box" , "one of many coach may have" .)