Meaning of UNSTABLE in English
un ‧ sta ‧ ble AC /ʌnˈsteɪb ə l/ BrE AmE adjective
1 . likely to change suddenly and become worse ⇨ instability :
The political situation is still very unstable.
an unstable relationship
2 . something that is unstable is likely to move or fall
3 . someone who is unstable changes very suddenly so that you do not know how they will react or behave:
a mentally unstable man
4 . an unstable chemical is likely to separate into simpler substances
• • •
▪ mentally ill having an illness that affects your mind and your behaviour:
Many mentally ill people are treated in the community.
He was declared mentally ill and unfit to stand trial.
▪ crazy informal mentally ill:
I couldn’t think straight. I felt like I was going crazy (=becoming crazy) .
▪ mad old-fashioned mentally ill. This word is now usually considered offensive, and is usually used in a different meaning, when you think that someone's ideas are not sensible:
Swift himself went mad (=became mad) later in life.
a mad old woman
▪ insane [not before noun] old-fashioned having a serious and permanent mental illness:
She went insane after her two young sons were murdered.
a hospital for the criminally insane
▪ disturbed not behaving in a normal way because of mental or emotional problems, especially problems that are caused by bad experiences:
She teaches emotionally disturbed children.
Her experiences left her deeply disturbed.
▪ unstable having an emotional state that often changes very suddenly:
Her mother was mentally unstable.
He lived in a small Putney flat with his ageing Aunt Bunny, and his emotionally unstable sister, Nancy.
He was too unstable to be a leader.
▪ deranged behaving in a crazy or dangerous way, usually because of being mentally ill:
A deranged young woman entered the school and took the life of one young boy.
▪ psychopathic having a serious and permanent mental illness that causes violent or criminal behaviour:
The film is about a psychopathic killer.
▪ psychotic suffering from or caused by a serious mental illness that changes your character and makes you unable to behave in a normal way:
psychiatric services for chronic psychotic patients.
There is a tendency for psychotic illnesses to be inherited.
▪ neurotic relating to or suffering from a mental illness that makes you unreasonably worried of frightened:
His mother was neurotic and insecure.
She's neurotic about her weight.
A bored or lonely horse may become so neurotic that it chases itself around in circles.
Longman Dictionary of Contemporary English. Longman - Словарь современного английского языка. 2012