Why Does The Expression 'Nuts' Mean Crazy?

Believe it or not, the definition of the word 'nuts' as 'crazy' has been around for quite a long time. In fact, the adjective "nutty" meaning insane was first recorded in the year 1821, so it was probably being used before that time.

This meaning of the word 'nuts' first came from the definition 'be nutts upon' (be very fond of) which was first recorded in 1785. The definition of nuts meaning crazy probably had its roots in the reference of a person's head to a nut because of its shape and size, e.g.1846 'to be off one's nut' (which references the head) also means 'to be insane' 1860.

One possible explanation of this meaning of the word nuts comes from the fact that nuts consist of a thick, hard outer shell and they are very hard to break into. If a person has lost their mind or gone crazy, then they are very difficult to deal with and rationalise with i.e. It is difficult to break into their mind to try and help them out. Although this theory is not concrete, it is definitely plausible.

The word nuts as crazy can also be used in the sense that you are 'nuts about someone', also meaning that you really like them or indeed love them. This probably comes from the common belief that when someone is in love, they tend to go a little bit crazy, in a good way of course, which then refers back to the original definition of nuts. Or it could also mean that a person is very enthusiastic about a particular phenomenon i.e. "he's just nuts about history".

For full explanations of the word nut in all contexts that it can be used in, including the recording dates of these definitions and any changes to the words meaning can be found at www.etymonline.com/index.php?l=n&p=9

The use of the word 'nuts' to signify somebody who is crazy is being used since very long time and the probable reason for the phenomenon is that a nut is covered with a hard shell that is mostly very difficult to break. Usually a person who is crazy is very difficult to deal with and same happen with a nut as it is difficult to deal with while breaking. So the reason sounds plausible to describe the phenomenon, although not concrete.

The word 'nuts' has some other uses also and when you are conjugating it with the term about it forms the term 'nuts about somebody' and the meaning it conveys is that of very much in love or very enthusiastic about some phenomenon.

Because when you eat nuts, you....
No, I don't know actually.

Nuts is a fruit?
"He went nuts when he got a dog!"