دیروز

دیروز is built from دی (di-), an Old Persian particle that survives in modern Persian as a "preceding-time" marker. The same particle produces دیشب (dīshab, "last night," literally "passed-night"), دیر (dīr, "late," "delayed"), and دی‌ماه (the Iranian month corresponding to December and January, the "passing" month of winter solstice). Persian's native time vocabulary is one of its oldest preserved word clusters, dating back to Old Persian inscriptions from the Achaemenid period (6th century BCE). While Persian later borrowed Arabic words for hours, minutes, and seconds (ساعت, دقیقه, ثانیه), the core day-words stayed Persian. This is consistent with how languages typically retain their oldest most-used vocabulary even after borrowing extensively in other domains. The pattern of compound time words (دیروز, امروز, فردا as "this/that/ahead day") also makes Persian time vocabulary feel like a small grid you can master in one sitting.