instability vs imbalance

instability and imbalance both are nouns.

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

As nouns, instability and imbalance are synonyms defined as:

Other synonyms of instability include unbalance.

instability (noun)	imbalance (noun)
the quality or attribute of being unstable and irresolute	lack of proportion; imbalance among the parts of something
unreliability attributable to being unstable	a lack of balance or state of disequilibrium
an unstable order
a lack of balance or state of disequilibrium