Frivolous, scatterbrained (7)
I believe the answer is:
flighty
I believe this clue is a double definition.
'frivolous' is the first definition.
(similar in meaning)
'scatterbrained' is the second definition.
(I know that scatterbrained can be written as flighty)
(Other definitions for flighty that I've seen before include "Mentally giddy, in an aerial way perhaps" , "Giddy-minded" , "Frivolous - irresponsible" , "Capricious" , "Fickle; erratic" .)