nuts

The modern slang meanings of 'nuts' derive from the early 20th-century American English phrase "off one's nut," where 'nut' was slang for 'head.' To be 'off one's nut' meant to be insane, a metaphor comparing a malfunctioning mind to a head that had come loose. By the 1930s, the adjective 'nuts' solidified, meaning crazy. The interjectional use, as in "Nuts to that!", likely stems from the association of 'nuts' with something worthless or contemptible, akin to dismissing something as mere nutshells. Thus, a simple term for a seed evolved through metaphorical extensions into a versatile slang term for madness, enthusiasm, or dismissal.

The word 'nuts' is a plural noun that has been converted into an adjective and interjection. Its core is the Old English noun 'hnutu', meaning the hard-shelled fruit.