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) metaphorically in a military sense: solid front
Part of Speech: noun neuter
Citing in TDNT: 7:609, 1077
From G4732; something established, that is, (abstractly) confirmation (stability): - stedfastness.
These two sites give similar information, with the definition from several dictionaries and statistics on the use of the word.
Perseus Digital Library
University of Chicago's Logion lexicon
Thayer's dictionary plus other information.
From this site's dictionary (in Italian)
Click on the first column to search for that word as a form of the root στερέωμα; click on the second column to search for that grammatical form of the root στερέωμα; click on the third column to search for that word and grammatical form; click on the total to search for the root στερέωμα.