непостоя́нный meaning in English — changeable, changeful, fickle

English meaning

changeable adj Likely to change often or unpredictably.
changeful adj Changing frequently; very susceptible to change
fickle adj Changing opinions, loyalties, or feelings often and without warning.
giddy adjective Feeling dizzy or unsteady, as if the head is spinning.
haphazard adj Done without any clear plan or order; disorganized and random.
inconsistent adj Not staying the same over time; unpredictable or unreliable.
inconstant adj Not constant; wavering.
uncertain adj Not sure or confident about something.
unsteady adj Not firmly balanced or supported; shaky.
variable adj Likely to change, or capable of being changed.
versatile adj Able to do many different things well, or adaptable to many different uses.
volatile adjective Likely to change suddenly and unpredictably, especially for the worse.

непостоя́нный is used for these senses in English:

changeable Subject to sudden or frequent changes.
changeful (rare) Changing frequently; very susceptible to change
fickle Quick to change one’s opinion or allegiance; insincere; not loyal or reliable.
giddy (predicative, _, only) Feeling a sense of spinning in the head, causing a perception of unsteadiness and being about to fall down; dizzy.
haphazard Random; chaotic; incomplete; not thorough, constant, or consistent.
inconstant Not constant; wavering.
uncertain Fitful or unsteady.
unsteady Inconstant in purpose, or volatile in behavior.