Vessel from Russia, or tank (5)
I believe the answer is:
aorta
'vessel' is the definition.
(blood vessel)
'from russia or tank' is the wordplay.
'from' indicates the answer is hidden within the clue.
'AORTA' is hidden in the letters of 'russia or tank'.
(Other definitions for aorta that I've seen before include "Heart's great artery" , "Main human artery" , "One leads from heart" , "Tube" , "Great artery in body" .)