Red Cross is in the market (7)
I believe the answer is:
marxist
'red' is the definition.
('marxist' can be a synonym of 'red')
'cross is in the market' is the wordplay.
'cross' becomes 'x'.
'in the' indicates putting letters inside.
'market' becomes 'mart' ('mart' can be a synonym of 'market').
'x'+'is'='xis'
'xis' put within 'mart' is 'MARXIST'.
(Other definitions for marxist that I've seen before include "Red" , "Revolutionary" , "left-wing" , "A leftie once" , "left-winger" .)