Letter from Europe takes time to reach Mark (6)
I believe the answer is:
stigma
'mark' is the definition.
('stigma' can be a synonym of 'mark')
'letter from europe takes time' is the wordplay.
'letter from europe' becomes 'sigma' (greek letter).
'takes' means one lot of letters goes inside another.
'time' becomes 't'.
'sigma' enclosing 't' is 'STIGMA'.
'to reach' is the link.
(Other definitions for stigma that I've seen before include "Blot" , "Badge of shame" , "Mark of infamy or disgrace" , "part of plant" , "Mark of shame or social disgrace" .)