minacious

from WordNet (r) 3.0 (2006)

minacious
    adj 1: threatening or foreshadowing evil or tragic developments;
           "a baleful look"; "forbidding thunderclouds"; "his tone
           became menacing"; "ominous rumblings of discontent";
           "sinister storm clouds"; "a sinister smile"; "his
           threatening behavior"; "ugly black clouds"; "the
           situation became ugly" [syn: {baleful}, {forbidding},
           {menacing}, {minacious}, {minatory}, {ominous},
           {sinister}, {threatening}]

from The Collaborative International Dictionary of English v.0.48

Minacious \Mi*na"cious\, a. [L. minax, -acis. See {Menace}.]
   Threatening; menacing. [R.]
   [1913 Webster]