Expanse

n. [Lat. expansum, from expansus, p. p. of expandere.] That which is expanded or spread out; a wide extent of space or body; especially, the arch of the sky; the firmament. Lights . . . high in the expanse of heaven. Milton. The smooth expanse of crystal lakes. Pope.

To expand. [Obs.] “That lies expansed unto the eyes of all.” Browne.