A person from Boston, or a type of igneous rock with specific mineral composition.
From 'Boston' + '-ite' (English suffix for inhabitants or for scientific/mineralogical terms). The geological sense comes from the rock being identified in the Boston area.
The suffix '-ite' works double duty in English—it creates both demonyms (Bostonite = person from Boston) and scientific terms (granite, felsite), which is why you sometimes can't tell if something refers to a person or a mineral.
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