firmament , n :
(usually uncountable, literary, poetic, also figurative) The vault of the heavens, where the clouds, sun, moon, and stars can be seen; the heavens, the sky. (countable) The field or sphere of an activity or interest. (uncountable, obsolete, astronomy, historical) In the geocentric Ptolemaic system, the eighth celestial sphere which carried the fixed stars; (countable, by extension) any celestial sphere. (uncountable, obsolete except biblical) The abode of God and the angels; heaven. (countable, obsolete) A piece of jewellery worn in a headdress with numerous gems resembling stars in the sky. (countable, obsolete, also figurative) A basis or foundation; a thing which lends strength or support. (countable, obsolete) The act or process of making firm or strengthening.