The Collaborative International Dictionary of English v.0.48:

Tonight \To*night"\, adv. [Prep. to + night]
   1. On this present or coming night.
      [1913 Webster]

   2. On the last night past. [Obs.] --Shak.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Tonight \To*night"\, n.
   The present or the coming night; the night after the present
   day.
   [1913 Webster]

WordNet (r) 3.0 (2006):

tonight
    adv 1: during the night of the present day; "drop by tonight"
           [syn: tonight, this evening, this night]
    n 1: the present or immediately coming night