The Collaborative International Dictionary of English v.0.48:

Portend \Por*tend"\, v. t. [imp. & p. p. Portended; p. pr. &
   vb. n. Portending.] [L. portendre, portentum, to foretell,
   to predict, to impend, from an old preposition used in comp.
   + tendere to stretch. See Position, Tend.]
   1. To indicate (events, misfortunes, etc.) as in future; to
      foreshow; to foretoken; to bode; -- now used esp. of
      unpropitious signs. --Bacon.
      [1913 Webster]

            Many signs portended a dark and stormy day.
                                                  --Macaulay.
      [1913 Webster]

   2. To stretch out before. [R.] "Doomed to feel the great
      Idomeneus' portended steel." --Pope.
      [1913 Webster]

   Syn: To foreshow; foretoken; betoken; forebode; augur;
        presage; foreshadow; threaten.
        [1913 Webster]

WordNet (r) 3.0 (2006):

portend
    v 1: indicate by signs; "These signs bode bad news" [syn:
         bode, portend, auspicate, prognosticate, omen,
         presage, betoken, foreshadow, augur, foretell,
         prefigure, forecast, predict]

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "portend":
   adumbrate, apprehend, augur, betoken, bode, call, croak, forebode,
   forecast, foreshadow, foreshow, foretoken, forewarn,
   give advance notice, have a premonition, have a presentiment,
   look black, lower, menace, omen, preapprehend, precaution, predict,
   premonish, prenotify, presage, prewarn, prognosticate, promise,
   prophesy, tell in advance, threaten, vaticinate, warn