The term aṣ̌a- stands in the centre of ancient Iranian thought. It is a pivotal concept in Zoroastrian religious lore, but is not, in its significance, coeval with Zoroastrianism. As an object of eschatological longing, aṣ̌a- has Indo-Iranian roots. It is, in Old and Middle Persian texts, primarily understood as a synecdoche for the divine sphere where the religiously dutiful expect to lead a blessed mental existence after death. Aṣ̌a- is also a deity of the Old Avestan pantheon, thus a deified concept. Finally, the term is regularly used in the Gāthās as both the authoritative instance of measuring human (religious) conduct, and the normative goal of therapeutic (eschatological) activity. In this latter usage, too, and in agreement with its form and etymology, aṣ̌a- signifies a concrete phenomenon. There are good reasons to think that this phenomenon is the world as it was “put together” by Ahura Mazdā, and only subsequently sickened by the forces of deception. Translations to date, such as “truth” and “order”, are examined, all of which are shown to have serious problems. In conclusion I propose to translate aṣ̌a- as “cosmos”.