Firmament

n.	1.	Fixed foundation; established basis. Custom is the . . . firmament of the law. - Jer. Taylor.
	2.	The region of the air; the sky or heavens. And God said, Let there be a firmament in the midst of the waters, and let it divide the waters from the waters. - Gen. i. 6. And God said, Let there be lights in the firmament. - Gen. i. 14.
	3.	(Old Astron.) The orb of the fixed stars; the most rmote of the celestial spheres.

Noun

1.

firmament - the apparent surface of the imaginary sphere on which celestial bodies appear to be projected Synonyms: celestial sphere, empyrean, heavens, vault of heaven, welkin, sphere

Caelus, air, azure, blue sky, caelum, canopy, canopy of heaven, cerulean, cope, empyrean, ether, heaven, heavens, hyaline, lift, lifts, sky, starry heaven, the blue, the blue serene, vault, vault of heaven, welkin