WordNet (r) 3.0 (2006):

jillion
    n 1: a very large indefinite number (usually hyperbole); "there
         were millions of flies" [syn: million, billion,
         trillion, zillion, jillion, gazillion]

Moby Thesaurus II by Grady Ward, 1.0:

58 Moby Thesaurus words for "jillion":
   a billion, a crore, a lakh, a million, a myriad, a nonillion,
   a quadrillion, a thousand, a zillion, astronomical number, billion,
   considerable, decillion, duodecillion, ever so many, full many,
   gobs, googol, googolplex, heap, heaped-up, infinitude, infinity,
   large number, loads, many, million, multifarious, multifold,
   multiple, multitudinal, multitudinous, myriad, no few, nonillion,
   not a few, novemdecillion, numerous, octillion, octodecillion,
   oodles, quadrillion, quantities, quattuordecillion, quindecillion,
   quintillion, quite some, septillion, sexdecillion, sextillion,
   slew, thousand, tredecillion, trillion, undecillion, very many,
   vigintillion, zillion