Fancy trifle (9)
I believe the answer is:
suspicion
This clue might be a double definition.
'fancy' is the first definition.
The definition and answer can be both related to thinking as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'trifle' is the second definition.
(thesaurus)
Can you help me to learn more?
(Other definitions for suspicion that I've seen before include "Hitchcock film" , "Suggestion" , "Trace" , "Little" , "Inkling" .)