Straw, essentially (4)
I believe the answer is:
tube
'straw essentially' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tube that I've seen before include "Pipe or hose" , "Cylindrical hollow conduit" , "Pack of toothpaste; type of train" , "Can of beer (colloquial)" , "Long, hollow cylinder" .)