What is Unstable ?
Unstable is adj 1. not stable They put scaffolding round the chimney be- cause it had become unstable. The weather can be very unstable in August. We have to take account of the very unstable exchange rate. 2. likely to change suddenly The eco- nomic situation has become very unstable. Neighbouring states were worried that the unstable military regime could be over- thrown. 3. with a mental state that is likely to change quickly The patient is mentally unstable.
source: Easier English, Student Dictionary Upper Intermediate Level