Ankāʾ is the air in which Allah manifests the bodies of the worlds within itself and by itself. (Istilāḥ, 537)
Ankāʾ is a metaphor for hayūlā (prime matter). For, like the ankāʾ, it cannot be seen; it is only present together with form. It is an intelligible entity. The absolute hayūlā, which is common to all bodies, is designated as the unsur-i aʿẓam (the greatest element). (Kāshānī, 133; Jāmiʿ, 90)