[syn: baleful, forbidding, menacing, minacious, minatory, ominous, sinister, threatening]
The Collaborative International Dictionary of English v.0.48:
Baleful \Bale"ful\ (b[=a]l"f[.u]l), a. [AS. bealoful. See Bale
   misery.]
   1. Full of deadly or pernicious influence; destructive.
      "Baleful enemies." --Shak.
      [1913 Webster]
            Four infernal rivers that disgorge
            Into the burning lake their baleful streams.
                                                  --Milton.
      [1913 Webster]
   2. Full of grief or sorrow; woeful; sad. [Archaic]
      [1913 Webster]
WordNet (r) 3.0 (2006):
baleful
    adj 1: deadly or sinister; "the Florida eagles have a fierce
           baleful look" [syn: baleful, baneful]
    2: 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]
Moby Thesaurus II by Grady Ward, 1.0:
82 Moby Thesaurus words for "baleful":
   apocalyptic, bad, baneful, bitchy, black, bodeful, boding,
   corroding, corrosive, corrupting, corruptive, counterproductive,
   cussed, damaging, dark, deadly, deleterious, detrimental, dire,
   direful, disadvantageous, disserviceable, distressing, doomful,
   dreary, evil, evil-starred, fateful, foreboding, gloomy, harmful,
   hateful, hurtful, ill, ill-boding, ill-fated, ill-omened,
   ill-starred, inauspicious, iniquitous, injurious, invidious,
   lethal, lowering, malefic, maleficent, malevolent, malicious,
   malign, malignant, mean, menacing, mischievous, nasty, noisome,
   noxious, of evil portent, ominous, ornery, pernicious, poisonous,
   portending, portentous, prejudicial, scatheful, sinister, somber,
   threatening, toxic, unfavorable, unfortunate, unlucky, unpromising,
   unpropitious, untoward, venenate, veneniferous, venenous, venomous,
   vicious, virulent, wicked