Swell copper and stone object (7)
I believe the answer is:
distend
'swell' is the definition.
(I know that distend is a more specific form of the action bloat)
'copper and stone object' is the wordplay.
'copper' becomes 'DI' (detective inspector, type of copper).
'and' says to put letters next to each other.
'stone' becomes 'st' (abbreviation).
'object' becomes 'end' (both can mean a goal or purpose).
'di'+'st'+'end'='DISTEND'
(Other definitions for distend that I've seen before include "Expand, inflate" , "blow up" , "Stretch" , "Fill out" , "Swell by pressure from within" .)