Fir"ma*ment (?), n. [L. firmamentum, fr. firmare to make firm: cf. F. firmament. See Firm, v. & a.]
1.
Fixed foundation; established basis.
[Obs.]
Custom is the . . . firmament of the law.
Jer. Taylor.
2.
The region of the air; the sky or heavens.
And God said, Let there be a firmament in the mist of the waters, and let it divide the waters from the waters.
Gen. i. 6.
And God said, Let there be lights in the firmament.
Gen. i. 14.
⇒ In Scripture, the word denotes an expanse, a wide extent; the great arch or expanse over out heads, in which are placed the atmosphere and the clouds, and in which the stars appear to be placed, and are really seen.
3. Old Astron.
The orb of the fixed stars; the most rmote of the celestial spheres.
© Webster 1913.