Ultimation is a widely applied term in the Omnidoxy that generally relates to the ultimate form or stage of a process, especially an intellectual or spiritual process. Specifically in the context of Astronist eschatology, ultimation is an important term that is applied to the process of cosmosis.

In Astronism, the ultimation, or the ultimate state, is the one in which a person has achieved cosmosis, either post-corporeal or corporeal, the former of which is seen as the lesser of the two due to its achievement by all upon death. However, the achievement of corporeal cosmosis is considered the ultimation in Astronism and is tantamount to the achievement of our limitation, which is referred to in the Epitaph of Astronism.

Other uses of the term are varied, one of which is in the subera known as the Quest for the Ultimation, a time period in the History of Astronism in which Cometan intensively searched for "the ultimation" to life as part of an existential, intellectual and spiritual journey.

In other contexts, the word ultimation may be used in reference to that which exists as the highest, most superior, or the final or most perfect form of something; the plural term is ultimations. The use of the word ultimatory relates to an ultimation, or ultimate state of something.

Much like the term's use in the context of the eschatology of Astronism, in the Astronist philosophy of religion, ultimation refers to the climatic goal of a religion; the state or process towards which faith, hope, action, and belief are all considered to be directed. As aforementioned, for Astronists, this ultimation is cosmosis, as achieved either through death in its simplest form by all or as achieved by fewer in the form of corporeal cosmosis.