One seen in paintings with gag getting vegetable (9)
I believe the answer is:
artichoke
'vegetable' is the definition.
(type of vegetable)
'one seen in paintings with gag' is the wordplay.
'one' becomes 'i' (Roman numeral).
'seen in' means one lot of letters goes inside another.
'paintings' becomes 'art' (painting is an art).
'with' says to put letters next to each other.
'gag' becomes 'choke' (synonyms).
'art'+'choke'='artchoke'
'i' going within 'artchoke' is 'ARTICHOKE'.
'getting' acts as a link.
(Other definitions for artichoke that I've seen before include "Vegetable could give you a thicko ear" , "Thistlelike edible flower head" , "Edible thistle-like bud" , "Thistle-like plant with edible heads" , "Jerusalem or globe?" .)