Russian autocrat's not left mark (5)
I believe the answer is:
stain
'mark' is the definition.
(I know that mark can be written as stain)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for stain that I've seen before include "Unsightly mark" , "Tarnish" , "Stigma" , "Satin (anag.)" , "Mark with colour, dirt" .)