instability vs undependability

instability and undependability both are nouns.

Word	Noun	Adjective	Verb	Adverb
instability	Yes	No	No	No
undependability	Yes	No	No	No

As nouns, undependability is a hypernym of instability; that is, undependability is a word with a broader meaning than instability:

Other hypernyms of instability include undependableness, unreliability, unreliableness.

instability (noun)	undependability (noun)
the quality or attribute of being unstable and irresolute	the trait of not being dependable or reliable
unreliability attributable to being unstable
an unstable order
a lack of balance or state of disequilibrium