Poke right inside compartment (4)
I believe the answer is:
prod
'poke' is the definition.
(synonyms)
'right inside compartment' is the wordplay.
'right' becomes 'r' (common abbreviation).
'inside' means one lot of letters goes inside another.
'compartment' becomes 'pod' (pod can mean a compartment or case).
'r' put into 'pod' is 'PROD'.
(Other definitions for prod that I've seen before include "Poke (with a finger, etc)" , "Stimulus" , "Poke with forefinger, stimulate" , "Spur or goad" , "Motivate; jab" .)