The Collaborative International Dictionary of English v.0.48:

Menace \Men"ace\ (m[e^]n"[asl]s; 48), v. t. [imp. & p. p.
   Menaced ([=a]st); p. pr. & vb. n. Menacing.] [OF.
   menacier, F. menacer. See Menace, n.]
   1. To express or show an intention to inflict, or to hold out
      a prospect of inflicting, evil or injury upon; to
      threaten; -- usually followed by with before the harm
      threatened; as, to menace a country with war.
      [1913 Webster]

            My master . . . did menace me with death. --Shak.
      [1913 Webster]

   2. To threaten, as an evil to be inflicted.
      [1913 Webster]

            By oath he menaced
            Revenge upon the cardinal.            --Shak.
      [1913 Webster]

WordNet (r) 3.0 (2006):

menacing
    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]

Moby Thesaurus II by Grady Ward, 1.0:

106 Moby Thesaurus words for "menacing":
   about to be, abusive, alarming, already in sight, apocalyptic,
   approaching, at hand, bad, baleful, baneful, black, bludgeoning,
   blustering, bodeful, boding, brewing, browbeating, bulldozing,
   bullying, chancy, close, close at hand, coming, comminatory,
   critical, dangerous, dangersome, dark, denunciatory, dire, doomful,
   dreary, evil, evil-starred, explosive, fateful, fear-inspiring,
   foreboding, forthcoming, fraught with danger, frightening, future,
   gathering, gloomy, going to happen, hazardous, hectoring, ill,
   ill-boding, ill-fated, ill-omened, ill-starred, immediate,
   imminent, impendent, impending, in danger imminent, in prospect,
   in reserve, in store, in the cards, in the offing, in the wind,
   in view, inauspicious, instant, intimidating, jeopardous, looming,
   lowering, lurking, minacious, minatory, near, near at hand,
   nearing, of evil portent, ominous, on the horizon, overhanging,
   parlous, periculous, perilous, portending, portentous, preparing,
   risky, serious, sinister, somber, terrifying, terroristic,
   terrorizing, that will be, threatening, threatful, to come, ugly,
   unfavorable, unfortunate, unlucky, unpromising, unpropitious,
   untoward, upcoming, waiting