(ف) نَصَحَ يَنْصَحُ نُصْحًا وَنَصِيْحَةًnaṣaḥa yanṣaḥu nuṣḥan wa-naṣīḥatan: to say or do something for another's good with no self-interest; hence (1) to give sincere counsel (2) to be pure, to be clear. ﴿اِذَا نَصَحُوْا لِلّٰهِ وَرَسُوْلِهِۦ﴾ (At-Tawbah 9:91); ﴿وَنَصَحْتُ لَكُمْ وَلٰكِنْ لَّا تُحِبُّوْنَ النّٰصِحِيْنَ﴾ (Al-Aʿrāf 7:79)
نُصْحٌnuṣḥ (verbal noun, maṣdar, also a noun, ism dhāt): sincere counsel, sincere goodwill. ﴿وَلَا يَنْفَعُكُمْ نُصْحِيْٓ﴾ (Hūd 11:34)
نَاصِحٌnāṣiḥ pl. نٰصِحُوْنَnāṣiḥūna (active participle, ism fāʿil): a sincere counsellor. ﴿وَاَنَا لَكُمْ نَاصِحٌ اَمِيْنٌ﴾ (Al-Aʿrāf 7:68); ﴿وَاِنَّا لَهُۥ لَنٰصِحُوْنَ﴾ (Yūsuf 12:11)
نَصُوْحٌnaṣūḥ (intensive form, ṣīghat al-mubālaghah, on the pattern of فَعُوْلٌfaʿūl): utterly sincere. Only once in the Quran: ﴿تُوْبُوْٓا اِلَي اللّٰهِ تَوْبَةً نَّصُوْحًا﴾ (At-Taḥrīm 66:8)