Source : Webster's Revised Unabridged Dictionary (1913)

Mattress \Mat"tress\, n. [OF. materas, F. matelas, LL.
   matratium; cf. Sp. & Pg. almadraque, Pr. almatrac; all from
   Ar. ma[.t]rah a place where anything is thrown, what is
   thrown under something, fr. [.t]araha to throw.]
   1. A quilted bed; a bed stuffed with hair, moss, or other
      suitable material, and quilted or otherwise fastened.
      [Written also {matress}.]

   2. (Hydraulic Engin.) A mass of interwoven brush, poles,
      etc., to protect a bank from being worn away by currents
      or waves.

Source : WordNet®

mattress
     n : a large thick pad filled with resilient material and often
         incorporating coiled springs, used as a bed or part of a
         bed