All his weight was on one foot, and he was in a state of unstable equilibrium.
Yes, indeed, yes; I know she's as unstable as water and as hard to hold as a puff of wind.
Moral standards are as unstable as the shifting sands of the sea.
We can see here very clearly how unstable a thing polytheism is.
They are unstable, improvident, easily discouraged, easily led astray.