The Collaborative International Dictionary of English v.0.48:

Premonitory \Pre*mon"i*to*ry\, a. [L. praemonitorius.]
   Giving previous warning or notice; as, premonitory symptoms
   of disease. -- Pre*mon"i*to*ri*ly, adv.
   [1913 Webster]

WordNet (r) 3.0 (2006):

premonitory
    adj 1: warning of future misfortune [syn: precursory,
           premonitory]

Moby Thesaurus II by Grady Ward, 1.0:

29 Moby Thesaurus words for "premonitory":
   augural, foreboding, forerunning, foreshadowing, foreshowing,
   foretokening, forewarning, heavy with meaning, indicative,
   intuitive, meaningful, monitory, ominous, portentous, precautional,
   precautionary, precursive, precursory, predictive, prefigurative,
   preindicative, presageful, presaging, prodromal, prodromic,
   prognostic, prognosticative, significant, warning