Inky smear (4)
I believe the answer is:
blot
'inky smear' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for blot that I've seen before include "Smudge of ink" , "Stain on 1 across?" , "Dry piece of writing" , "Cross out; inky mess" , "Smudge (on escutcheon?)" .)