Old irrational socialist ran out (7)
I believe the answer is:
expired
'ran out' is the definition.
('expire' can be a synonym of 'run out')
'old irrational socialist' is the wordplay.
'old' becomes 'ex' (prefix meaning former or onetime).
'irrational' becomes 'pi' (an irrational number).
'socialist' becomes 'red' (red can informally mean a socialist).
'ex'+'pi'+'red'='EXPIRED'
(Other definitions for expired that I've seen before include "Deceased" , "Died; elapsed" , "Ran out or died" , "Became invalid" , "Run out" .)