Firmament comes from Old French firmament, from Latin firmamentum ('a support, the sky'), from firmare ('to make firm'), from firmus ('firm, stable'); the word renders Greek stereoma in the Septuagint's account of the vault of heaven. The development is chiefly a borrowing or learned continuation, carrying an older form and meaning into English rather than building the word from a purely native base. In present use, it is used as a noun meaning "the vault of the sky regarded as a solid expanse; the heavens", so the historical material remains connected with the current sense rather than standing as bare ancestry. The wider English family includes related forms such as firm, affirm, and confirm, showing how the same historical material continues to organize neighboring vocabulary. The named historical forms include Latin firmamentum and Latin firmus, keeping the history tied to concrete forms rather than a loose resemblance. Its semantic neighborhood includes sky, heavens, heaven, and welkin, locating the modern specialization without adding a new origin story.