na-adjective, noun
unstable; insecure; precarious
Describes physical, emotional, economic, or systemic lack of stability. The gloss 'crankiness' is a rare, informal extension for a person's mood.
この机は脚が不安定で、少し揺れる。
This desk is unstable because its legs are a bit wobbly.
彼は
He has been emotionally unstable lately.
政情不安定な国では投資リスクが高い。
Investment risk is high in countries with political instability.