The Institutional Dictionary of Astronism is the cumulation of receptions between Cometan and the astronomical world during the Founding era (2013-2021). The publication of this very first full-length Institutional Dictionary of Astronism represents eight years of the development of Astronism from its inception to how it stands today in 2021. The publication of this dictionary also encapsulates Astronism exactly as it exists now and how Cometan conceives it by the end of the Founding era. This dictionary and its contents capture what Astronism is now for posterity to look back on how this astronomical belief system will change as time progresses. Many of the words and definitions of this dictionary will alter as we enter the Establishment era and Astronism continues its progression in becoming world religion. However, what will not ever change is Cometan’s absolute devotion to the stars of the night sky and his discovery of their secrets through his receptions, personal inspirations, and his overall relationship with The Great Cosmos.