Spot Greek character crossing junction (6)
I believe the answer is:
stigma
'spot' is the definition.
(thesaurus)
'greek character crossing junction' is the wordplay.
'greek character' becomes 'sigma' (letter from the Greek alphabet).
'crossing' means one lot of letters goes inside another.
'junction' becomes 't'.
'sigma' placed around 't' is 'STIGMA'.
(Other definitions for stigma that I've seen before include "Part of a flower" , "Bad mark" , "Disgraceful mark" , "evidence of nastiness?" , "Mark of shame, stain on reputation" .)