Vertiginous (5)
I believe the answer is:
giddy
'vertiginous' is the definition.
(I know that vertiginous can be written as giddy)
This is the entire clue.
(Other definitions for giddy that I've seen before include "Dizzy - flighty" , "Frivolous -- liable to fall" , "Dizzy or frivoloous" , "Frivolous - in a spin?" , "Faint - excited" .)