firmament

Short definition from Wiktionary

Noun

1. 1
   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; (countable, by extension) any celestial sphere.
4. 4
   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.
6. 6
   A basis or foundation; a support.
7. 7
   The act or process of making firm or strengthening.