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

Moby Thesaurus II by Grady Ward, 1.0:

24 Moby Thesaurus words for "tonight":
   as of now, as things are, at present, at this juncture,
   at this moment, at this point, at this time, but now, even now,
   for the nonce, for this occasion, here, here and now, hereat,
   hic et nunc, in our time, in these days, just now, now, nowadays,
   on the spot, this day, this night, today