He takes a bow, promoted in police department (5)
I believe the answer is:
cupid
'he takes a bow' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'promoted in police department' is the wordplay.
'promoted' becomes 'up' (moving up).
'in' means one lot of letters goes inside another.
'police department' becomes 'CID' (abbreviation for Criminal Investigation Department).
'up' inserted into 'cid' is 'CUPID'.
Can you help me to learn more?
(Other definitions for cupid that I've seen before include "Armed boy" , "Tiny archer as Roman god of love" , "Roman god of love, child archer" , "Roman Eros" , "Boy with wings, bow, arrow" .)