Source : Webster's Revised Unabridged Dictionary (1913)

Sofa \So"fa\, n.; pl. {Sofas}. [Ar. soffah, from saffa to
   dispose in order: cf. F. sofa, It. sof[`a].]
   A long seat, usually with a cushioned bottom, back, and ends;
   -- much used as a comfortable piece of furniture.

         Let fall the curtains, wheel the sofa round. --Cowper.

   {Sofa bed}, a sofa so contrived that it may be extended to
      form a bed; -- called also {sofa bedstead}.