expanse

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A wide and open extent, as of surface, land, or sky.
• noun Expansion.
• noun The distance or amount of expansion.

from The Century Dictionary.

• To expand; stretch out.
• Expanded; spread out.
• Separate; single: said especially of years in old planetary tables.
• noun Spatial or superficial extension; an uninterrupted stretch or area, especially one of considerable extent.
• noun Specifically In zoology, the extent or stretch of wing; the distance from tip to tip when the wings, as of an insect or a bird, are fully expanded. Also called alar expanse or extent.
• noun Enlargement; extension; expansion.
• noun Synonyms See extent.

from the GNU version of the Collaborative International Dictionary of English.

• noun That which is expanded or spread out; a wide extent of space or body; especially, the arch of the sky.
• transitive verb obsolete To expand.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A wide stretch, usually of sea, sky, or land.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the extent of a 2-dimensional surface enclosed within a boundary
• noun a wide scope
• noun a wide and open space or area as of surface or land or sky