In Scripture the word denotes an expanse, a wide extent; for such is the signification of the Hebrew word. The original, therefore, does not convey the sense of solidity, but of stretching, extension; the great arch of 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. --Webster.
[N] indicates this entry was also found in Nave's Topical Bible
[E] indicates this entry was also found in Easton's Bible Dictionary
Bibliography InformationSmith, William, Dr. "Entry for 'Firmament'". "Smith's Bible Dictionary".