nut

The word carries a duality between hard physical structures and mental instability or obsession. In its botanical and mechanical senses, it evokes images of hardness, containment, and security. When applied to people, the connotation shifts based on context. It can be derogatory, suggesting someone is "crazy" or mentally unstable (often implying a chaotic or unpredictable nature). Conversely, in modern informal usage, it often describes an intense, singular passion. Calling someone a "fitness nut" typically conveys a sense of obsessive dedication rather than mental illness, often with a slightly playful or admiring tone.