Remark companion's missed by complete accident (9)
I believe the answer is:
utterance
'remark' is the definition.
(I've seen this before)
'companion's missed by complete accident' is the wordplay.
'companion' becomes 'ch' (Companion of Honour).
'missed by' indicates named letters should be taken away.
'complete' becomes 'utter' (both can mean total).
'accident' becomes 'chance' (I've seen this in other clues).
'utter'+'chance'='utterchance'
'utterchance' with 'ch' removed is 'UTTERANCE'.
(Other definitions for utterance that I've seen before include "Expression in speech" , "Word" , "Something said" , "one's said" , "Remark" .)