ص ف ص فṣ-f-ṣ-f
(quadriliteral, rubāʿī) — صَفْصَفٌṣafṣaf: a perfectly level and bare plain with no rise or dip in it; the lexicographers say it is a reduplication of ṣ f f, as though the earth were made as even as a single row. Only once in the Quran, and that after the mountains are blown away on the Day of Resurrection: ﴿فَيَذَرُهَا قَاعًا صَفْصَفًا﴾ (Ṭā Hā 20:106)