Tenacity of Greek with sex appeal! (4)
I believe the answer is:
grit
'tenacity' is the definition.
(thesaurus)
'greek with sex appeal' is the wordplay.
'greek' becomes 'gr'.
'with' means one lot of letters go next to another.
'sex appeal' becomes 'it'.
'gr'+'it'='GRIT'
'of' is the link.
(Other definitions for grit that I've seen before include "Kind of courage or dirt" , "Coarse stone or sand" , "Fortitude" , "Determination - small bits of stone" , "Small loose particles of stone" .)