An Etymological Dictionary of the German Language/Hitze
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Hitze, f., ‘heat, ardour, passion,’ from the equiv. MidHG. hitze, OHG. hizza, f. (for *hitja, the Goth. form); comp. Du. hitte, hette, OIc. hite, m., ‘heat’; all formed by the weakest stage of gradation from the stem of the adj. heiß (Teut. root hī̆t, hait, ‘hot’). OHG. hizza was adopted by Rom. (comp. Ital. izza, ‘anger, indignation’).