Channel is unswerving, we hear (6)
I believe the answer is:
strait
'channel' is the definition.
(strait is a kind of channel)
'unswerving we hear' is the wordplay.
'unswerving' becomes 'straight' ('straight' can be a synonym of 'unswerving').
'we hear' shows a homophone (sound like).
'straight' sounds like 'STRAIT'.
'is' is the link.
(Other definitions for strait that I've seen before include "Difficult position" , "Narrow sorts of traits" , "Narrow sort of traits (6)" , "Narrow kind of traits" , "Narrow strip of water between two larger ones" .)