Nothing in painting a major vessel? (5)
I believe the answer is:
aorta
'major vessel?' is the definition.
(I've seen this before)
'nothing in painting a' is the wordplay.
'nothing' becomes 'O' (looks like zero - 0).
'in' means one lot of letters goes inside another.
'painting' becomes 'art' (I've seen this before).
'o' put within 'art' is 'aort'.
'aort'+'a'='AORTA'
(Other definitions for aorta that I've seen before include "vital transporter" , "Major artery of the body" , "Large trunk artery" , "Bloody channel" , "Main human artery" .)