Unemotional police officer many backed (6)
I believe the answer is:
stolid
'unemotional' is the definition.
(similar in meaning)
'police officer many backed' is the wordplay.
'police officer' becomes 'di' (detective inspector).
'many' becomes 'lots' (lots of something).
'backed' is a reversal indicator.
'di'+'lots'='dilots'
'dilots' written backwards gives 'STOLID'.
(Other definitions for stolid that I've seen before include "Wooden" , "Calm, unanimated" , "Showing little or no interest or emotion" , "Difficult to excite, apathetic" , "Impassive or apathetic" .)