Endlessly put off covering a mark and smear (6)
I believe the answer is:
defame
'smear' is the definition.
(I've seen this before)
'endlessly put off covering a mark' is the wordplay.
'endlessly' means to remove the last letter.
'put off' becomes 'defer' ('defer' can be a synonym of 'put off').
'covering' indicates putting letters inside.
'a mark' becomes 'am' (I can't explain this - if you can you should believe this answer much more).
'defer' with its last letter taken away is 'defe'.
'defe' going around 'am' is 'DEFAME'.
'and' is the link.
Can you help me to learn more?
(Other definitions for defame that I've seen before include "'Denigrate, slander (6)'" , "Calumniate, slander" , "Attack good reputation, speak ill of" , "Injure the reputation of" , "Run down" .)