Firmament

The modern English word heaven is derived from the earlier (Middle English) heven (attested 1159); this in turn was developed from the previous Old English form heofon.

By about 1000, heofon was being used in reference to the Christianized "place where God dwells",

but originally, it had signified "sky, firmament"^[2] (e.g. in Beowulf, c. 725).