Flattering remark made by companion, we hear (10)
I believe the answer is:
compliment
'flattering remark' is the definition.
(a complimentary remark)
'companion we hear' is the wordplay.
'companion' becomes 'complement' (both mean something that goes with something else).
'we hear' indicates a 'sounds like' (homophone) clue.
'complement' is a homophone of 'COMPLIMENT'.
'made by' is the link.
(Other definitions for compliment that I've seen before include "Commend, flatter" , "Expression of polite admiration" , "pat on the back" , "Word of appreciation" , "Politely congratulate" .)