Firmament

from the Vulgate firmamentum, which is used as the translation
of the Hebrew "raki'a". This word means simply "expansion." It
denotes the space or expanse like an arch appearing immediately
above us. They who rendered "raki'a" by firmamentum regarded it
as a solid body. The language of Scripture is not scientific but
popular, and hence we read of the sun rising and setting, and
also here the use of this particular word. It is plain that it
was used to denote solidity as well as expansion. It formed a
division between the waters above and the waters below (Gen.
1:7). The "raki'a" supported the upper reservoir (Ps. 148:4). It
was the support also of the heavenly bodies (Gen. 1:14), and is
spoken of as having "windows" and "doors" (Gen. 7:11; Isa.
24:18; Mal. 3:10) through which the rain and snow might descend.