The Collaborative International Dictionary of English v.0.48:

Overwhelming \O`ver*whelm"ing\, a.
   Overpowering; irresistible. -- O`ver*whelm"ing*ly, adv.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Overwhelm \O`ver*whelm"\, v. t. [imp. & p. p. Overwhelmed; p.
   pr. & vb. n. Overwhelming.]
   [1913 Webster]
   1. To cover over completely, as by a great wave; to overflow
      and bury beneath; to ingulf; hence, figuratively, to
      immerse and bear down; to overpower; to crush; to bury; to
      oppress, etc., overpoweringly.
      [1913 Webster]

            The sea overwhelmed their enemies.    --Ps. lxxviii.
                                                  53.
      [1913 Webster]

            Fearfulness and trembling are come upon me, and
            horror hath overwhelmed me.           --Ps. lv. 5.
      [1913 Webster]

            Foul deeds will rise,
            Though all the earth o'erwhelm them.  --Shak.
      [1913 Webster]

            Gaza yet stands; but all her sons are fallen,
            All in a moment overwhelmed and fallen. --Milton.
      [1913 Webster]

   2. To project or impend over threateningly.
      [1913 Webster]

            His louering brows o'erwhelming his fair sight.
                                                  --Shak.
      [1913 Webster]

   3. To cause to surround, to cover. --Papin.
      [1913 Webster]

WordNet (r) 3.0 (2006):

overwhelming
    adj 1: so strong as to be irresistible; "an overpowering need
           for solitude"; "the temptation to despair may become
           overwhelming"; "an overwhelming majority" [syn:
           overpowering, overwhelming]
    2: very intense; "politics is his consuming passion";
       "overwhelming joy" [syn: consuming, overwhelming]