The Collaborative International Dictionary of English v.0.48:

Punch \Punch\, n. [Hind. p[=a]nch five, Skr. pa?can. So called
   because composed of five ingredients, viz., sugar, arrack,
   spice, water, and lemon juice. See Five.]
   A beverage composed of wine or distilled liquor, water (or
   milk), sugar, and the juice of lemon, with spice or mint; --
   specifically named from the kind of spirit used; as rum
   punch, claret punch, champagne punch, etc.
   [1913 Webster]

   Milk punch, a sort of punch made with spirit, milk, sugar,
      spice, etc.

   Punch bowl, a large bowl in which punch is made, or from
      which it is served.

   Roman punch, a punch frozen and served as an ice.
      [1913 Webster]

WordNet (r) 3.0 (2006):

milk punch
    n 1: a punch made of spirits and milk and sugar and spices