Communist in company displays 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 is a kind of communist).
'in' means one lot of letters goes inside another.
'company' becomes 'co' (abbreviation).
'red' going inside 'co' is 'CREDO'.
'displays' is the link.
(Other definitions for credo that I've seen before include "Apostles' beliefs" , "Statement of faith" , "Doctrine or belief" , "piece of sacred music" , "set of ideas" .)