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Adjective: portentous  por'ten-tus
  1. Of momentous or ominous significance
    "such a raised all my curiosity";
    - prodigious
  2. Ominously prophetic
    - fateful, foreboding
  3. Puffed up with vanity
    "a portentous and boastful manner";
    - grandiloquent, overblown, pompous, pontifical

See also: important, pretentious, prophetic, prophetical, significant