Vessel I'm not sure we included (4)
I believe the answer is:
ewer
'vessel' is the definition.
(ewer is a kind of vessel)
'i'm not sure we included' is the wordplay.
'i'm not sure' becomes 'er' (expression of hesitation).
'included' indicates putting letters inside.
'er' placed around 'we' is 'EWER'.
(Other definitions for ewer that I've seen before include "Were (anag)" , "Pitcher, water jug" , "A wide-mouthed water jug" , "Large pitcher" , "Oversized jug" .)