(ض) قَسَطَ يَقْسِطُ قَسْطًا وَقُسُوْطًاqasaṭa yaqsiṭu qasṭan wa-qusūṭan: to deviate from what is right, to act unjustly.
قَاسِطٌqāsiṭ pl. قٰسِطُوْنَqāsiṭūna (active participle, ism fāʿil): one who acts unjustly. ﴿وَاَمَّا الْقٰسِطُوْنَ فَكَانُوْا لِجَهَنَّمَ حَطَبًا﴾ (Al-Jinn 72:15)
قِسْطٌqisṭ (noun, ism dhāt): a rightful share, justice, equity. ﴿كُوْنُوْا قَوّٰمِيْنَ بِالْقِسْطِ﴾ (An-Nisāʾ 4:135); اَقْسَطُaqsaṭu (elative, ism tafḍīl): more just.
Form IV (ifʿāl) اَقْسَطَ يُقْسِطُ اِقْسَاطًاaqsaṭa yuqsiṭu iqsāṭan: to act justly (hamzah of removal, hamzat al-salb: to remove injustice).
مُقْسِطٌmuqsiṭ pl. مُقْسِطِيْنَmuqsiṭīna (active participle, ism fāʿil): one who acts justly. ﴿وَاَقْسِطُوْا اِنَّ اللّٰهَ يُحِبُّ الْمُقْسِطِيْنَ﴾ (Al-Ḥujurāt 49:9) Note: the bare form in the sense of injustice and the verb form (bāb) ifʿāl in the sense of justice — two opposite meanings from a single root.