KJV Dictionary Definition: firmament
FIRMAMENT, n. ferm'ament. L. firmamentum, from firmus, firmo.
The region of the air; the sky or heavens. In scripture, the word denotes an expanse, a wide extent; for such is the signification of the Hebrew word, coinciding with regio, region, and reach. The original therefore does not convey the sense of solidity, but of stretching, extension; the great arch or expanse over our heads, in which are placed the atmosphere and the clouds, and in which the stars appear to be placed, and are really seen.
And God said, Let there be a firmament in the midst of the waters, and let it divide the waters from the waters. Gen. 1:6.
And God said, Let there be lights in the firmament.
FIRMAMENT'AL, a. Pertaining to the firmament; celestial; being of the upper regions.