Channel not crooked we hear (6)
I believe the answer is:
strait
'channel' is the definition.
(strait is a kind of channel)
'not crooked we hear' is the wordplay.
'not crooked' becomes 'straight' ('straight' is the opposite to 'crooked').
'we hear' shows a homophone (sound like).
'straight' is a homophone of 'STRAIT'.
(Other definitions for strait that I've seen before include "Sound" , "Narrow passage joining two large areas of water" , "'Bering or Gibraltar, say (6)'" , "Difficult state for artist" , "Narrow stretch of water as at Gibraltar" .)