Firmament

имя существительное [поэтическое] (the firmament) небесный свод

Большой англо-русский словарь

Firmament

noun Etymology: Middle English, from Late Latin and Latin; Late Latin firmamentum, from Latin, support, from firmare 1. the vault or arch of the sky; heavens 2. obsolete basis 3. the field or sphere of an interest or activity Example: the international fashion firmamentfirmamental adjective

Merriam-Webster's Collegiate Dictionary