firmament

noun

1. 1.(usually uncountable) The vault of the heavens, where the clouds, sun, moon, and stars can be seen; the heavens, the sky.
2. 2.The field or sphere of an activity or interest.
3. 3.In the geocentric Ptolemaic system, the eighth celestial sphere which carried the fixed stars; (by extension) any celestial sphere.
4. 4.(obsolete except biblical) The abode of God and the angels; heaven.
5. 5.A piece of jewellery worn in a headdress with numerous gems resembling stars in the sky.