A trifle upset, dear? Drop round (8)
I believe the answer is:
falderal
'a trifle' is the definition.
(I have seen 'Flimsy trifle ' mean 'falderal' so perhaps 'trifle' could also mean 'falderal')
'upset dear? drop round' is the wordplay.
'upset' indicates an anagram.
'drop' becomes 'fall' ('fall' can be a synonym of 'drop'**).
'round' indicates putting letters inside.
'dear' anagrammed gives 'dera'.
'dera' going into 'fall' is 'FALDERAL'.
(Other definitions for falderal that I've seen before include "bother" , "Flimsy trifle" , "All fared (anag) - nonsense" .)