The process or state of being joined or united together; fusion or combination into one.
From coadunate + -ion (Latin suffix -io creating nouns from verbs). The noun form that captures the abstract concept of joining or fusion. Common in medieval medical and botanical terminology.
In Renaissance anatomy, 'coadunation' was the word for how separate tissues fused together during development or healing—it's a poetic way to describe what we now call biological fusion or integration.
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