Empyrean comes from Medieval Latin empyreum, from Ancient Greek empýrios ('in the fire, fiery'), from en- ('in') + pŷr ('fire'); in cosmology the highest heaven, a region of pure fire or light. Morphologically, the form is compositional: en- marks part of the visible structure, while the remaining element supplies the lexical base. In present use, it is used as a noun and adjective meaning "the highest heaven, or the sky; the celestial realm", so the historical material remains connected with the current sense rather than standing as bare ancestry. The wider English family includes derivatives such as empyreal and related forms such as empyreal, pyre, and pyro, showing how the same historical material continues to organize neighboring vocabulary. The named historical forms include Ancient Greek empýrios and Ancient Greek pŷr, keeping the history tied to concrete forms rather than a loose resemblance.