The Collaborative International Dictionary of English v.0.48:

Serenade \Ser`e*nade"\, n. [F. s['e]r['e]nade, It. serenata,
   probably fr. L. serenus serene (cf. Serene), misunderstood
   as a derivative fr. L. serus late. Cf. Soir['e]e.] (Mus.)
   (a) Music sung or performed in the open air at nights; --
       usually applied to musical entertainments given in the
       open air at night, especially by gentlemen, in a spirit
       of gallantry, under the windows of ladies.
   (b) A piece of music suitable to be performed at such times.
       [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Serenade \Ser`e*nade"\, v. t. [imp. & p. p. Serenaded; p. pr.
   & vb. n. Serenading.]
   To entertain with a serenade.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Serenade \Ser`e*nade"\, v. i.
   To perform a serenade.
   [1913 Webster]

WordNet (r) 3.0 (2006):

serenade
    n 1: a musical composition in several movements; has no fixed
         form [syn: divertimento, serenade]
    2: a song characteristically played outside the house of a woman
    v 1: sing and play for somebody; "She was serenaded by her
         admirers"