Source : Webster's Revised Unabridged Dictionary (1913)

Snowball \Snow"ball`\, n.
   1. A round mass of snow pressed or roller together, or
      anything resembling such a mass.

   2. (Bot.) The Guelder-rose.

   {Snowball tree} (Bot.), the Guelder-rose.

Snowball \Snow"ball`\, v. t. [imp. & p. p. {Snowballed}; p. pr.
   & vb. n. {Snowballing}.]
   To pelt with snowballs; to throw snowballs at.

Snowball \Snow"ball`\, v. i.
   To throw snowballs.

Source : WordNet®

snowball
     n 1: plant having heads of fragrant white trumpet-shaped flowers;
          grows in sandy arid regions [syn: {sweet sand verbena},
          {Abronia elliptica}]
     2: ball of ice cream covered with coconut and usually chocolate
        sauce
     3: ball of crushed ice with fruit syrup
     4: snow pressed into a ball for throwing (playfully)
     v 1: increase or accumulate at a rapidly accelerating rate
     2: throw snowballs at