Inconstancy is a related term of flightiness.
As nouns the difference between inconstancy and flightiness
is that inconstancy is lack of constancy; lack of consistency in thought, emotion or action while flightiness is the quality of being flighty.
inconstancy
English
Noun
(
inconstancies)
Lack of constancy; lack of consistency in thought, emotion or action.
-
flightiness
English
Noun
(-)
The quality of being flighty.