Unstable rhymes with:
stable, stable, table, abel, abell, able, cable, chaebol, crable, disable, enable, fable, frable, gable, grable, graybeal, hable, intercable, kable, knable, label, laible, mabel, mable, mislabel, raible, relabel, sable, schaible, stable, table, unable, waibel, zabel
Unstable sounds like:
unjustifiable, unjustifiably, unstoppable, unsuitable