Companion consumed, swallowed by pig (6)
I believe the answer is:
shadow
'companion' is the definition.
(I have seen 'Inseparable companion ' mean 'shadow' so perhaps 'companion' could also mean 'shadow')
'consumed swallowed by pig' is the wordplay.
'consumed' becomes 'had' ('have' can be a synonym of 'consume').
'swallowed by' means one lot of letters goes inside another.
'pig' becomes 'sow' (I've seen this before).
'had' put within 'sow' is 'SHADOW'.
(Other definitions for shadow that I've seen before include "Image cast - dog" , "Inseparable companion; dark patch" , "Dark area - follow secretly" , "Follow - dark patch" , "Dark shape (on the Opposition front bench?)" .)