στερέωμα, -τος, τό (< στερεόω), [in LXX: Refs Gen.1:6 ff., Psa.19:1 150:1, Eze.1:22-26 10:1 13:5, Dan LXX, TH Dan.3:56, Dan.12:3 (רָקִיעַ), Deu.33:26 (שַׁחַק), Refs Psa.18:2 71:3 (סֶלַע), Est.9:29, I Est.8:78 (82), Refs Sir.43:1, 8, 1Ma.9:14 * ;] a solid body; __(a) a support, foundation (Arist., al.); metaph., strength (Refs Psa.17:1-15 70:1-5, 1Mac, ll. with); steadfastness, firmness: τ. πίστεως, Col.2:5; __(b) the dome of heaven (believed to be a solid canopy), the firmament (LXX).† (AS)
Thayer:
1) that which has been made firm 1a) the firmament, the arch of the sky, which in early times was thought to be solid 1a1) a fortified place 1b) that which furnishes a foundation 1b1) on which a thing rests firmly, support 1c) firmness, steadfastness 1c1) metaph. in a military sense: solid front
στερέωμα
stereōma
ster-eh'-o-mah
From G4732; something established, that is, (abstractly) confirmation (stability)