flighty
Concise Oxford English Dictionary © 2008 Oxford University Press:
flighty/ˈflʌɪti/
▶adjective (flightier, flightiest) fickle and irresponsible.
– derivatives
flightily adverb,
flightiness noun.
flightily adverb,
flightiness noun.
'flighty' also found in these Oxford entries:

