- The definition of instability is a lack of stability or balance, or a tendency towards unpredictable or erratic behavior.
When you swing from one emotion to another, first feeling happy and then very sad for no reason, this is an example of emotional instability.
- lack of stability; unstableness; specif.,
- lack of firmness or steadiness
- lack of determination; irresolution
- tendency to behave or react violently or erratically: the instability of a chemical compound, emotional instability
(countable and uncountable, plural instabilities)