Scintilla of doubt (9)
I believe the answer is:
suspicion
This clue is a double definition.
'scintilla' is the first definition.
(thesaurus)
'doubt' is the second definition.
(I know that suspicion is a type of doubt)
'of' acts as a link.
(Other definitions for suspicion that I've seen before include "Misgiving, doubt" , "Hunch" , "Hitchcock film" , "Inkling" , "Suggestion" .)