Firm incorporating Soviet principles? (5)
I believe the answer is:
credo
'principles?' is the definition.
(I've seen this before)
'firm incorporating soviet' is the wordplay.
'firm' becomes 'co' (a firm is a company).
'incorporating' is an insertion indicator.
'soviet' becomes 'red' (red can informally mean communist).
'co' going around 'red' is 'CREDO'.
(Other definitions for credo that I've seen before include "System of principles" , "Dogma" , "Belief system" , "piece of sacred music" , "Words of believer" .)