Aqueduct, essentially (5)
I believe the answer is:
canal
'aqueduct essentially' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for canal that I've seen before include "Man-made channel of water" , "Artificial waterway as at Panama (5)" , "eg Grand Union" , "Manmade flower" , "Artificial waterway for barges" .)