Expanse

Part of speech: noun (n.)

That which is expanded or spread out; a wide extent of space or body; especially, the arch of the sky. "The green expanse." Savage. Lights . . . high in the expanse of heaven. Milton. The smooth expanse of crystal lakes. Pope.

Part of speech: verb (v.)

To expand. [Obs.] That lies expansed unto the eyes of all. Sir. T. Browne.