Mark is new saint (5)
I believe the answer is:
stain
'mark' is the definition.
('stain' can be a synonym of 'mark')
'new saint' is the wordplay.
'new' is an anagram indicator.
'saint' is an anagram of 'STAIN'.
'is' is the link.
(Other definitions for stain that I've seen before include "Smear" , "Blemish; colour (wood)" , "Mark with colour, dirt" , "Black mark for saint" , "Spot - shame" .)