The Collaborative International Dictionary of English v.0.48:

Flood \Flood\ (fl[u^]d), n. [OE. flod a flowing, stream, flood,
   AS. fl[=o]d; akin to D. vloed, OS. fl[=o]d, OHG. fluot, G.
   flut, Icel. fl[=o][eth], Sw. & Dan. flod, Goth. fl[=o]dus;
   from the root of E. flow. [root]80. See Flow, v. i.]
   1. A great flow of water; a body of moving water; the flowing
      stream, as of a river; especially, a body of water,
      rising, swelling, and overflowing land not usually thus
      covered; a deluge; a freshet; an inundation.
      [1913 Webster]

            A covenant never to destroy
            The earth again by flood.             --Milton.
      [1913 Webster]

   2. The flowing in of the tide; the semidiurnal swell or rise
      of water in the ocean; -- opposed to ebb; as, young
      flood; high flood.
      [1913 Webster]

            There is a tide in the affairs of men,
            Which, taken at the flood, leads on to fortune.
                                                  --Shak.
      [1913 Webster]

   3. A great flow or stream of any fluid substance; as, a flood
      of light; a flood of lava; hence, a great quantity widely
      diffused; an overflowing; a superabundance; as, a flood of
      bank notes; a flood of paper currency.
      [1913 Webster]

   4. Menstrual disharge; menses. --Harvey.
      [1913 Webster]

   Flood anchor (Naut.), the anchor by which a ship is held
      while the tide is rising.

   Flood fence, a fence so secured that it will not be swept
      away by a flood.

   Flood gate, a gate for shutting out, admitting, or
      releasing, a body of water; a tide gate.

   Flood mark, the mark or line to which the tide, or a flood,
      rises; high-water mark.

   Flood tide, the rising tide; -- opposed to ebb tide.

   The Flood, the deluge in the days of Noah.
      [1913 Webster]

WordNet (r) 3.0 (2006):

the Flood
    n 1: (Biblical) the great deluge that is said in the Book of
         Genesis to have occurred in the time of Noah; it was
         brought by God upon the earth because of the wickedness of
         human beings [syn: Noah's flood, Noachian deluge, Noah
         and the Flood, the Flood]