We don't have synonyms for skyboxes yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are skybox and hayboxes.
(n) :
(video games, computer graphics) A cube with textures on its inner faces, used to simulate the sky or similar backdrop around a three-dimensional playfield.
(n) :
(video games, computer graphics) A cube with textures on its inner faces, used to simulate the sky or similar backdrop around a three-dimensional playfield.