The quality or state of being coessential; sharing the same essential nature or substance with something else.
From co- (together) + essential (from Latin essentialis, from essentia meaning 'being' or 'essence') + -ness (suffix forming abstract nouns). The prefix co- was added to essential to create coessential in medieval philosophy to describe things sharing identical fundamental nature.
Medieval theologians loved this word when debating the nature of the Trinity—they used 'coessentialness' to argue that the Father, Son, and Holy Spirit shared the same fundamental divine essence, which was a mind-bending way to solve a religious puzzle.
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