Other forms: nuts
In DIY, a nut is the small threaded ring that a bolt screws into. Tighten the nut, a nut and bolt, the nut has come loose.
It is named for the shape and hardness of the food. That older sense is the fruit with a hard shell — a walnut, a bag of nuts — and nut allergy is one of the commonest phrases in the language now. Informally, a nut is somebody eccentric or obsessive: a football nut. Note nuts and bolts, meaning the practical details, and a hard nut to crack, meaning a difficult problem or a tough person.
1nounnutThe threaded ring a bolt tightens into.
“The nut had worked loose over about a year.”
2nounfruitA fruit with a hard shell and an edible kernel.
“There were nuts and dried fruit in a bowl by the door.”
3nounobsessiveSomebody obsessive about something.
“He is a complete railway nut.”
Too few real examples of this word to estimate which sense is commonest.
nut is a small hard thing.
Old English hnutu is Germanic and related to Latin nux, the source of nutrition's cousin nucleus — a kernel. The engineering nut is the food word borrowed for a small hard object, which is how most tool names are made.
Middle English
note
English, today
nut
From Middle English note. From Middle English note, nute, from Old English hnutu, from Proto-West Germanic hnut, from Proto-Germanic hnuts (“nut”), from a root knu- possibly shared with Proto-Celtic knūs and Latin nux (“nut”). Based on the form of the nouns and the restriction of the root to Germanic, Celtic and Italic, it has been argued to be of non-Indo-European (qfa-sub -) origin. See also West Frisian nút, Dutch noot, German Nuss, Danish nød, Swedish nöt, Norwegian nøtt*.
Etymology from Wiktionary, CC BY-SA