The Arabic word ʿadl (justice) comes from the root verb ‘a-d-l, which means to be equal to, just, straight, and temperate.
The term ʿadl is used in the Qur’an in the following senses:
To act justly or equitably, to be fair in judgment, to be impartial in speech, or witness; to straighten someone to a state of moral uprightness, or from disbelief to faith, to offer a compensation in place of punishment for a sin, to deviate or turn away from the truth, or to set up something as equal to something else, which can have a positive connotation approximating the first of these, or a negative one referring to the sin of shirk, worshipping anything else alongside God.
Al-Iṣfahānī’s definition of justice:
Justice [al-ʿadl] is a term associated with equality [musāwāh]. It has various meanings, depending on the context. In the context of potential, it is an innate human desire for equality. In the context of action, it means dealing fairly with others. And in the context of the Divine, it describes the complete orderliness of God’s actions. In the pursuit of justice, man tries to be virtuous, but can only be perfectly virtuous if his outer actions stem from an inner noble disposition and character. Outwardly just actions do not necessarily make one a just human being. If the intention of the just action is for the sake of show, a worldly benefit, or fear of a Sultan’s punishment, it cannot be truly just.
The opposite of justice (ʿadl), is injustice (ẓulm), from the verb ẓalama, which the Qur’an uses to refer to the one wronged (Q. 22:39) and to be denied one’s due (Q. 21: 47). Justice in the Qur’anic context is about conforming to the divine law and being obedient to God. Justice in the Qur’an has no room for discrimination based on color, race, or gender. Qur’anic justice is a moral virtue and a legal concept. These two dimensions of justice—justice towards oneself and justice towards others—are two sides of the same coin, so should not be separated. Those in leadership positions should be the embodiment of moral virtue if they are to dispense justice in a fair manner.