Futility of a fictitious fair (6)
I believe the answer is:
vanity
'futility' is the definition.
(thesaurus)
'a fictitious fair' is the wordplay.
I cannot quite see how this works, but
'a' could be 'an' and 'an' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
'of' acts as a link.
Can you help me to learn more?
(Other definitions for vanity that I've seen before include "Conceit about one's appearance" , "Conceitedness, self-love" , "Thackery was the author of ''. . . . . . Fair''" , "Excessive self-regard" , "Excessive pride in one's appearance" .)