Instability

n. unsteadiness, shakiness, lack of firmness; changeability, tendency to behave erratically

Instability in systems is generally characterized by some of the outputs or internal states growing without bounds. Not all systems that are not stable are unstable; systems can also be marginally stable or exhibit limit cycle behavior.In control theory, a system is unstable if any of the roots of its characteristic equation has real part greater than zero. This is equivalent to any of the eigenvalues of the state matrix having real part greater than zero.In structural engineering, a structure can become unstable when excessive load is applied. Beyond a certain threshold, structural deflections magnify stresses, which in turn increases deflections. This can take the form of buckling or crippling. The general field of study is called structural stability.
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Instability /in·sta·bil·i·ty/ lack of steadiness or stability. detrusor instability involuntary contraction of the detrusor muscle of the bladder [more]Instability - Community and Resources

Noun
1. an unstable order
(antonym) stability
(hypernym) disorder
2. unreliability attributable to being unstable
(hypernym) undependability, undependableness, unreliability, unreliableness
3. a state of disequilibrium (as may occur in cases of inner ear disease)
(synonym) imbalance, unbalance
(hypernym) disequilibrium
4. the quality or attribute of being unstable and irresolute
(synonym) unstableness
(antonym) stability, stableness
(hypernym) unsteadiness
(hyponym) shakiness, ricketiness

(n.)
The quality or condition of being unstable; want of stability, firmness, or steadiness; liability to give way or to fail; insecurity; precariousness; as, the instability of a building.
  

(n.)
Lack of determination of fixedness; inconstancy; fickleness; mutability; changeableness; as, instability of character, temper, custom, etc.