(ن) صَدَقَ يَصْدُقُ صِدْقًاṣadaqa yaṣduqu ṣidqan: to speak the truth, to make true; it takes its object directly (truthfulness means that heart and tongue are in accord, that speech conforms to fact and that action conforms to word). ﴿رِجَالٌ صَدَقُوْا مَا عَاهَدُوا اللّٰهَ عَلَيْهِ﴾ (Al-Aḥzāb 33:23)
صَادِقٌṣādiq (active participle, ism fāʿil): truthful, one who makes true. ﴿وَكُوْنُوْا مَعَ الصّٰدِقِيْنَ﴾ (At-Tawbah 9:119)
اَصْدَقُaṣdaqu (elative, ism tafḍīl): more truthful. ﴿وَمَنْ اَصْدَقُ مِنَ اللّٰهِ حَدِيْثًا﴾ (An-Nisāʾ 4:87)
صِدْقٌṣidq (also a noun, ism dhāt): truth, truthfulness. ﴿وَالَّذِيْ جَآءَ بِالصِّدْقِ وَصَدَّقَ بِهِۦٓ﴾ (Az-Zumar 39:33)
صِدِّيْقٌṣiddīq (adjective): utterly truthful, perfectly sincere. ﴿اِنَّهُۥ كَانَ صِدِّيْقًا نَّبِيًّا﴾ (Maryam 19:41)
صَدِيْقٌṣadīq (adjective): friend. ﴿اَوْ صَدِيْقِكُمْ﴾ (An-Nūr 24:61)
صَدَقَةٌṣadaqah pl. صَدَقٰتٌṣadaqāt (noun, ism dhāt): relinquishing one's own right, a thing given to someone beyond his due, alms (it is the manifestation of truthfulness in practice, and the word ṣadaqah is used both for obligatory alms, i.e. zakāh, and for voluntary alms). ﴿اِنَّمَا الصَّدَقٰتُ لِلْفُقَرَآءِ وَالْمَسٰكِيْنِ﴾ (At-Tawbah 9:60)
صَدُقَةٌṣaduqah pl. صَدُقٰتٌṣaduqāt: a woman's dower. ﴿وَاٰتُوا النِّسَآءَ صَدُقٰتِهِنَّ نِحْلَةً﴾ (An-Nisāʾ 4:4)
Form II (tafʿīl) صَدَّقَ يُصَدِّقُ تَصْدِيْقًاṣaddaqa yuṣaddiqu taṣdīqan: to declare someone truthful, to declare a thing true, to confirm; its object takes the preposition bi.
مُصَدِّقٌmuṣaddiq (active participle, ism fāʿil): one who confirms. ﴿وَاٰمِنُوْا بِمَآ اَنْزَلْتُ مُصَدِّقًا لِّمَا مَعَكُمْ﴾ (Al-Baqarah 2:41)
Form V (tafaʿʿul) تَصَدَّقَ يَتَصَدَّقُ تَصَدُّقًاtaṣaddaqa yataṣaddaqu taṣadduqan (original form), اِصَّدَّقَ يَصَّدَّقُ اِصَّدُّقًاiṣṣaddaqa yaṣṣaddaqu iṣṣadduqan (altered form; both are permissible): to relinquish one's own right, to give another more than his due, to give alms.
تَصَدَّقْtaṣaddaq (imperative, amr): give more, give alms; مُتَصَدِّقٌmutaṣaddiq (active participle, ism fāʿil): one who gives alms. ﴿وَتَصَدَّقْ عَلَيْنَا ۭ اِنَّ اللّٰهَ يَجْزِي الْمُتَصَدِّقِيْنَ﴾ (Yūsuf 12:88); ﴿اِنَّ الْمُصَّدِّقِيْنَ وَالْمُصَّدِّقٰتِ﴾ (Al-Ḥadīd 57:18)