The Collaborative International Dictionary of English v.0.48:

Nonce \Nonce\ (n[o^]ns), n. [For the nonce, OE. for the nones, a
   corruption of for then ones, where n. in then is a relic of
   AS. m in [eth]am, dat. of the article and demonstrative
   pronoun, E. the. See For, Once, and The.]
   The one or single occasion; the present call or purpose; --
   chiefly used in the phrase

   for the nonce, i. e. for the present time.
      [1913 Webster]

            The miller was a stout carl for the nones.
                                                  --Chaucer.
      [1913 Webster]

            And that he calls for drink, I 'll have prepared him
            A chalice for the nonce.              --Shak.
      [1913 Webster]

   Nonce word, "a word apparently employed only for the
      nonce". --Murray (New English Dict.).
      [1913 Webster]

WordNet (r) 3.0 (2006):

nonce
    n 1: the present occasion; "for the nonce" [syn: time being,
         nonce]

Moby Thesaurus II by Grady Ward, 1.0:

31 Moby Thesaurus words for "nonce":
   contemporaneity, contemporaneousness, historical present,
   modernity, newness, now, nowadays, nowness, our times, present,
   present tense, presentness, the Now Generation, the nonce, the now,
   the present, the present age, the present day, the present hour,
   the present juncture, the present time, the time being, the times,
   these days, this day, this hour, this instant, this moment,
   this point, this stage, today