Main route all but fixed from here (6)
I believe the answer is:
seaway
'main route' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'all but fixed from here' is the wordplay.
'all but' means to remove the last letter ('all but' can mean 'almost' or 'nearly').
'fixed' becomes 'set' (both can mean decided or determined).
'from here' becomes 'away' (I've seen this in another clue).
'set' with its last letter taken off is 'se'.
'se'+'away'='SEAWAY'
Can you help me to learn more?
(Other definitions for seaway that I've seen before include "Channel for shipping" , "Channel open to ships" , "Inland route for use by seagoing ships" , "Ship route" , "Route for a vessel" .)