Experiencing a tropical fever or delirium, especially affecting sailors in hot climates, causing them to jump overboard believing water is a green field.
From Spanish 'calentura' (fever), derived from Latin 'calens' (hot). The term originally described a specific tropical disease that affected sailors and evolved to mean any feverish delirium or madness.
Sailors would literally hallucinate and jump into the ocean thinking it was grass—this word captured such a real maritime nightmare that doctors actually debated whether calenture was a distinct disease or just extreme heat exposure!
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