Source : Webster's Revised Unabridged Dictionary (1913)

Spinach \Spin"ach\, Spinage \Spin"age\, n. [OF. espinache,
   espinoche, F. ['e]pinard; cf. F. spinace, Sp. espinaca; all
   fr. Ar. isf[=a]n[=a]j, isfin[=a]j, aspan[=a]kh, probably of
   Persian origin.] (Bot.)
   A common pot herb ({Spinacia oleracea}) belonging to the
   Goosefoot family.

   {Mountain spinach}. See {Garden orache}, under {Orache}.

   {New Zealand spinach} (Bot.), a coarse herb ({Tetragonia
      expansa}), a poor substitute for spinach.

   Note: Various other pot herbs are locally called spinach.

Source : WordNet®

Tetragonia expansa
     n : coarse sprawling Australasian plant with red or yellow
         flowers; cultivated for its edible young shoots and
         succulent leaves [syn: {New Zealand spinach}, {Tetragonia
         tetragonioides}]