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English definition of “unstable”

unstable

adjective uk   /ʌnˈsteɪ.bl̩/ us  
not solid and firm and therefore not strong, safe, or likely to last: That chair looks a bit unstable to me. It is a poor and politically unstable society.Unsafe and insecure describes someone who suffers from sudden and extreme changes in their mental and emotional state: emotionally unstableOf unsound mindStupid and silly
(Definition of unstable from the Cambridge Advanced Learners Dictionary & Thesaurus © Cambridge University Press)
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