c.1250, from L.
firmamentum "firmament," lit. "a support or strengthening," from
firmus "firm" (see
firm (adj.)), used in Vulgate to translate Gk.
stereoma "firm or solid structure," which translated Heb.
raqia, a word used of both the vault of the sky and the floor of the earth in the O.T., probably lit. "expanse," from
raqa "to spread out," but in Syriac meaning "to make firm or solid," hence the erroneous translation.