Plural of calculus; stone-like deposits in the body (like kidney stones) or the mathematical field of infinitesimal analysis.
From Latin calculus meaning 'pebble' or 'small stone.' The plural form calculi directly follows Latin pluralization rules, as in 'stimulus/stimuli.'
It's wild that the same word calculi means both kidney stones in medicine AND the mathematical tool Newton and Leibniz invented—both involve accumulations (of minerals, of infinitesimal quantities), showing how metaphors shape scientific language.
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