(of people or ideas) slightly crazy, in a harmless way a batty old man Her mum’s completely batty. There was a batty old woman living next door. Synonymsmadcrazy nuts batty out of your mind (not) in your right mindThese are all informal words that describe somebody who has a mind that does not work normally.mad (informal, especially British English) having a mind that does not work normally:I thought I’d go mad if I stayed any longer. Mad is an informal word used to suggest that somebody’s behaviour is very strange, often because of extreme emotional pressure. It is offensive if used to describe somebody suffering from a real mental illness; use mentally ill instead. Mad is not usually used in this meaning in North American English; use crazy instead.crazy (informal, ) having a mind that does not work normally:A crazy old woman rented the upstairs room. Like mad, crazy is offensive if used to describe somebody suffering from a real mental illness.nuts [not before noun] (informal) mad:That noise is driving me nuts! You guys are nuts!batty (informal, especially British English) slightly mad, in a harmless way:Her mum’s completely batty.out of your mind (informal) unable to think or behave normally, especially because of extreme shock or anxiety:She was out of her mind with grief.(not) in your right mind (informal) (not) mentally normal:No one in their right mind would choose to work there.Patterns to be mad/crazy/nuts/out of your mind/not in your right mind to do something to go mad/crazy/nuts/batty to drive somebody mad/crazy/nuts/batty/out of their mind completely mad/crazy/nuts/batty/out of your mind See related entries: Describing strange traits Word Origin early 20th cent.: from bat (the animal) + -y.