Copper, officer who inspires devotion? (4)
I believe the answer is:
cult
'who inspires devotion?' is the definition.
(you might be devoted to a cult)
'copper officer' is the wordplay.
'copper' becomes 'Cu' (Cu is the chemical symbol for copper).
'officer' becomes 'lt' (abbreviation for lieutenant).
'cu'+'lt'='CULT'
(Other definitions for cult that I've seen before include "they believe" , "Esoteric religion" , "unorthodox organisation" , "Unorthodox or false religion" , "System of religious beliefs and rituals" .)