The Collaborative International Dictionary of English v.0.48:

Rarebit \Rare"bit\ (r[^a]r"b[i^]t), n.
   A dainty morsel; a Welsh rabbit. See Welsh rabbit, under
   Rabbit.
   [1913 Webster]

WordNet (r) 3.0 (2006):

rarebit
    n 1: cheese melted with ale or beer served over toast [syn:
         Welsh rarebit, Welsh rabbit, rarebit]

The Devil's Dictionary (1881-1906):

RAREBIT, n.  A Welsh rabbit, in the speech of the humorless, who point
out that it is not a rabbit.  To whom it may be solemnly explained
that the comestible known as toad-in-a-hole is really not a toad, and
that _riz-de-veau a la financiere_ is not the smile of a calf prepared
after the recipe of a she banker.