The Collaborative International Dictionary of English v.0.48:

Portent \Por*tent"\ (?; 277), n. [L. portentum. See Portend.]
   That which portends, or foretoken; esp., that which portends
   evil; a sign of coming calamity; an omen; a sign. --Shak.
   [1913 Webster]

         My loss by dire portents the god foretold. --Dryden.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

60 Moby Thesaurus words for "portent":
   adumbration, advance notice, augury, auspice, balefulness,
   banefulness, betokening, betokenment, bodefulness, boding,
   direness, doomfulness, fatality, fatefulness, foreboding,
   foreshadow, foreshadowing, foreshowing, foretoken, foretokening,
   forewarning, indicant, indication, marvel, meaning, miracle, omen,
   ominousness, phenomenon, plenty of notice, portentousness,
   precautioning, prefiguration, preindication, premonition,
   premonitory shiver, premonitory sign, premonitory symptom,
   prenotice, prenotification, presage, presagefulness, presentiment,
   presignifying, prewarning, prodigy, prognostic, prognostication,
   promise, sensation, shadow, sign, significance, sinisterness,
   soothsay, stunner, suggestiveness, token, tokening, type