Communist in company creates belief (5)
I believe the answer is:
credo
'belief' is the definition.
(credo is a kind of belief)
'communist in company' is the wordplay.
'communist' becomes 'red' (red can informally mean communist).
'in' indicates putting letters inside.
'company' becomes 'co' (abbreviation).
'red' going inside 'co' is 'CREDO'.
'creates' acts as a link.
(Other definitions for credo that I've seen before include "Mass movement" , "Faith - I believe" , "mission statement" , "Formal statement of belief" , "Guiding principles" .)