The Collaborative International Dictionary of English v.0.48:

Malevolent \Ma*lev"o*lent\, a. [L. malevolens, -entis; male ill
   + volens, p. pr. of velle to be willing or disposed, to wish.
   See Malice, and Voluntary.]
   Wishing evil; disposed to injure others; rejoicing in
   another's misfortune.
   [1913 Webster]

   Syn: Ill-disposed; envious; mischievous; evil-minded;
        spiteful; malicious; malignant; rancorous.
        [1913 Webster]

WordNet (r) 3.0 (2006):

malevolent
    adj 1: wishing or appearing to wish evil to others; arising from
           intense ill will or hatred; "a gossipy malevolent old
           woman"; "failure made him malevolent toward those who
           were successful"
    2: having or exerting a malignant influence; "malevolent stars";
       "a malefic force" [syn: malefic, malevolent, malign,
       evil]

Moby Thesaurus II by Grady Ward, 1.0:

87 Moby Thesaurus words for "malevolent":
   acrid, antagonistic, antipathetic, bad, baleful, baneful,
   belligerent, bitchy, bitter, black, caustic, clashing, colliding,
   conflicting, corroding, corrosive, corrupting, corruptive,
   counterproductive, criminal, damaging, deadly, deleterious,
   despiteful, detrimental, disadvantageous, disserviceable,
   distressing, evil, evil-disposed, full of hate, harmful, hateful,
   hostile, hurtful, ill, ill-affected, ill-conditioned, ill-disposed,
   ill-intentioned, ill-natured, improper, inaccurate, inauspicious,
   inexpedient, inferior, injurious, invalid, lethal, malefic,
   maleficent, malicious, malign, malignant, mischievous, noisome,
   noxious, ominous, peccant, pernicious, poisonous, prejudicial,
   quarrelsome, rancorous, repugnant, scatheful, set against, sinful,
   sinister, sore, spiteful, toxic, unfavorable, unhealthy, unkind,
   unpleasant, unskillful, untoward, venenate, veneniferous, venenous,
   venomous, vicious, virulent, vitriolic, wicked, wrong