Source : Webster's Revised Unabridged Dictionary (1913)

Spacious \Spa"cious\, a. [L. spatiousus: cf. F. spacieux. See
   {Space}, n.]
   1. Extending far and wide; vast in extent. ``A spacious plain
      outstretched in circuit wide.'' --Milton.

   2. Inclosing an extended space; having large or ample room;
      not contracted or narrow; capacious; roomy; as, spacious
      bounds; a spacious church; a spacious hall. --
      {Spa"cious*ly}, adv. -- {Spa"cious*ness}, n.

Source : WordNet®

spaciousness
     n : spatial largeness (especially inside a building) [syn: {capaciousness},
          {roominess}, {commodiousness}]