Bamboo vessel, not round (4)
I believe the answer is:
cane
'bamboo' is the definition.
(cane-producing plant)
'vessel not round' is the wordplay.
'vessel' becomes 'canoe' (canoe is a kind of vessel).
'not' suggests deleting specific letters.
'round' becomes 'o' (o is a circular letter).
'canoe' with 'o' taken away is 'CANE'.
(Other definitions for cane that I've seen before include "Kind of sugar?" , "Raspberry stem; beat" , "A light rod once used for punishment" , "Slender support for a plant" , "Slender stick" .)