expansen.[From L. expansus, p. p. of expandere. See Expand.] That which is expanded or spread out; a wide extent of space or body; especially, the arch of the sky.(Savage.)Lights . . . high in the expanse of heaven. (Milton.)The smooth expanse of crystal lakes. (Pope.)v. t. To expand.()That lies expansed unto the eyes of all. (Sir. T. Browne.)