Source : Webster's Revised Unabridged Dictionary (1913)

Drain \Drain\, v. t. [imp. & p. p. {Drained}; p. pr. & vb. n.
   {Draining}.] [AS. drehnigean to drain, strain; perh. akin to
   E. draw.]
   1. To draw off by degrees; to cause to flow gradually out or
      off; hence, to cause the exhaustion of.

            Fountains drain the water from the ground adjacent.
                                                  --Bacon.

            But it was not alone that the he drained their
            treasure and hampered their industry. --Motley.

   2. To exhaust of liquid contents by drawing them off; to make
      gradually dry or empty; to remove surface water, as from
      streets, by gutters, etc.; to deprive of moisture; hence,
      to exhaust; to empty of wealth, resources, or the like;
      as, to drain a country of its specie.

            Sinking waters, the firm land to drain, Filled the
            capacious deep and formed the main.   --Roscommon.

   3. To filter.

            Salt water, drained through twenty vessels of earth,
            hath become fresh.                    --Bacon.

Draining \Drain"ing\, vb. n. of {Drain}, v. t. (Agric.)
   The art of carrying off surplus water, as from land.

   {Draining tile}. Same as {Draintile}.

Source : WordNet®

draining
     adj : having a debilitating effect; "an exhausting job in the hot
           sun" [syn: {exhausting}]