Question about Picaroon's singular flights of fancy (6)
I believe the answer is:
whimsy
'flights of fancy' is the definition.
(whimsical thoughts or behaviour)
'question about picaroon's singular' is the wordplay.
'question' becomes 'why' (why is a question word).
'about' means one lot of letters goes inside another.
'picaroon's' becomes 'I'm' (where the crossword setter is 'Picaroon').
'singular' becomes 's' (abbreviation in grammar).
'im'+'s'='ims'
'why' going around 'ims' is 'WHIMSY'.
(Other definitions for whimsy that I've seen before include "Gentle fantasy" , "Odd or fanciful idea" , "Something fanciful" , "Fanciful ideas" , "Fancy; notion" .)