(ض) ثَنٰى يَثْنِيْ ثَنْيًاthanā yathnī thanyan: to double a thing, to fold, to bend. ﴿اَلَآ اِنَّهُمْ يَثْنُوْنَ صُدُوْرَهُمْ﴾ (Hūd 11:5)
اِثْنَانِithnāni / ثَانٍthān: two; second. ﴿ثَانِيَ اثْنَيْنِ اِذْ هُمَا فِي الْغَارِ﴾ (At-Tawbah 9:40)
مَثْنٰىmathnā (on the pattern مَفْعَلٌmafʿal, original form مَثْنَيٌmathnay): two by two, to repeat. ﴿مَثْنٰى وَثُلٰثَ وَرُبٰعَ﴾ (An-Nisāʾ 4:3)
مَثَانِيْmathānī (on the pattern مَفَاعِلُmafāʿilu, plural of مَثْنًيmathnany): repeated again and again, being in pairs. ﴿سَبْعًا مِّنَ الْمَثَانِيْ﴾ (Al-Ḥijr 15:87)
Form X (istifʿāl) اِسْتَثْنٰى يَسْتَثْنِيْ اِسْتِثْنَاءًistathnā yastathnī istithnāʾan: to set someone apart from a rule, to exempt; to say اِنْ شَآءَ اللّٰهُin shāʾa al-lāh. ﴿وَلَا يَسْتَثْنُوْنَ﴾ (Al-Qalam 68:18)