The Collaborative International Dictionary of English v.0.48:

Lemonade \Lem`on*ade"\ (l[e^]m`[u^]n*[=a]d"), n. [F. limonade;
   cf. Sp. limonada, It. limonata. See Lemon.]
   A beverage consisting of lemon juice mixed with water and
   sweetened. "If you have lemons, make lemonade"
   [1913 Webster]

WordNet (r) 3.0 (2006):

lemonade
    n 1: sweetened beverage of diluted lemon juice