Source : Webster's Revised Unabridged Dictionary (1913)

Wassail \Was"sail\, a.
   Of or pertaining to wassail, or to a wassail; convivial; as,
   a wassail bowl. ``Awassail candle, my lord, all tallow.''
   --Shak.

   {Wassail bowl}, a bowl in which wassail was mixed, and placed
      upon the table. ``Spiced wassail bowl.'' --J. Fletcher.
      ``When the cloth was removed, the butler brought in a huge
      silver vessel . . . Its appearance was hailed with
      acclamation, being the wassail bowl so renowned in
      Christmas festivity.'' --W. Irving.

   {Wassail cup}, a cup from which wassail was drunk.

Wassail \Was"sail\, n. [AS. wes h[=a]l (or an equivalent form in
   another dialect) be in health, which was the form of drinking
   a health. The form wes is imperative. See {Was}, and
   {Whole}.]
   1. An ancient expression of good wishes on a festive
      occasion, especially in drinking to some one.

            Geoffrey of Monmouth relates, on the authority of
            Walter Calenius, that this lady [Rowena], the
            daughter of Hengist, knelt down on the approach of
            the king, and, presenting him with a cup of wine,
            exclaimed, Lord king w[ae]s heil, that is,
            literally, Health be to you.          --N. Drake.

   2. An occasion on which such good wishes are expressed in
      drinking; a drinking bout; a carouse. ``In merry wassail
      he . . . peals his loud song.'' --Sir W. Scott.

            The king doth wake to-night and takes his rouse,
            Keeps wassail.                        --Shak.

            The victors abandoned themselves to feasting and
            wassail.                              --Prescott.

   3. The liquor used for a wassail; esp., a beverage formerly
      much used in England at Christmas and other festivals,
      made of ale (or wine) flavored with spices, sugar, toast,
      roasted apples, etc.; -- called also {lamb's wool}.

            A jolly wassail bowl, A wassail of good ale. --Old
                                                  Song.

   4. A festive or drinking song or glee. [Obs.]

            Have you done your wassail! 'T is a handsome, drowsy
            ditty, I'll assure you.               --Beau. & Fl.

Wassail \Was"sail\, v. i.
   To hold a wassail; to carouse.

         Spending all the day, and good part of the night, in
         dancing, caroling, and wassailing.       --Sir P.
                                                  Sidney.

Source : WordNet®

wassail
     n : a punch made of sweetened ale or wine heated with spices and
         roasted apples; especially at Christmas
     v 1: celebrate noisily, often indulging in drinking; engage in
          uproarious festivities; "The members of the wedding
          party made merry all night"; "Let's whoop it up--the
          boss is gone!" [syn: {revel}, {racket}, {make whoopie},
          {make merry}, {make happy}, {whoop it up}, {jollify}]
     2: propose a toast to; "Let us toast the birthday girl!";
        "Let's drink to the New Year" [syn: {toast}, {drink}, {pledge},
         {salute}]