Blot last bit of text in Greek letter (6)
I believe the answer is:
stigma
'blot' is the definition.
(I've seen this before)
'last bit of text in greek letter' is the wordplay.
'last bit of' suggests the final letters.
'in' indicates putting letters inside.
'greek letter' becomes 'sigma' (letter from the Greek alphabet**).
The final letter of 'text' is 't'.
't' going inside 'sigma' is 'STIGMA'.
(Other definitions for stigma that I've seen before include "Disgraceful sign" , "Part of a flower" , "Badge of shame" , "Bad mark" , "Mark of shame, stain on reputation" .)