Mid 16th century; earliest use found in William Alley (d. 1570), bishop of Exeter. From post-classical Latin empyreum (also empireum) fiery heaven or sphere of fire, use as noun (short for caelum empyreum fiery heaven) of neuter of empyreus fiery.
Definition of empyreum in US English:
empyreum
noun
Empyrean.
Origin
Mid 16th century; earliest use found in William Alley (d. 1570), bishop of Exeter. From post-classical Latin empyreum (also empireum) fiery heaven or sphere of fire, use as noun (short for caelum empyreum fiery heaven) of neuter of empyreus fiery.