The Collaborative International Dictionary of English v.0.48:

Threat \Threat\ (thr[e^]t), n. [AS. [thorn]re['a]t, akin to
   [=a][thorn]re['o]tan to vex, G. verdriessen, OHG. irdriozan,
   Icel. [thorn]rj[=o]ta to fail, want, lack, Goth.
   us[thorn]riutan to vex, to trouble, Russ. trudite to impose a
   task, irritate, vex, L. trudere to push. Cf. Abstruse,
   Intrude, Obstrude, Protrude.]
   The expression of an intention to inflict evil or injury on
   another; the declaration of an evil, loss, or pain to come;
   menace; threatening; denunciation.
   [1913 Webster]

         There is no terror, Cassius, in your threats. --Shak.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Threat \Threat\, v. t. & i. [OE. [thorn]reten, AS.
   [thorn]re['a]tian. See Threat, n.]
   To threaten. [Obs. or Poetic] --Shak.
   [1913 Webster]

         Of all his threating reck not a mite.    --Chaucer.
   [1913 Webster]

         Our dreaded admiral from far they threat. --Dryden.
   [1913 Webster]

WordNet (r) 3.0 (2006):

threat
    n 1: something that is a source of danger; "earthquakes are a
         constant threat in Japan" [syn: menace, threat]
    2: a warning that something unpleasant is imminent; "they were
       under threat of arrest"
    3: declaration of an intention or a determination to inflict
       harm on another; "his threat to kill me was quite explicit"
    4: a person who inspires fear or dread; "he was the terror of
       the neighborhood" [syn: terror, scourge, threat]

Moby Thesaurus II by Grady Ward, 1.0:

55 Moby Thesaurus words for "threat":
   admonishment, admonition, alarm, breakers ahead, cardhouse,
   cause for alarm, caution, caveat, commination, crisis, danger,
   dangerous ground, deterrent example, emergency, endangerment,
   example, final notice, final warning, foreboding, forewarning,
   gaping chasm, gathering clouds, hazard, hint, house of cards,
   imperilment, intimation, intimidation, jeopardy, lesson, menace,
   monition, moral, notice, notification, object lesson, omen, pass,
   peril, pinch, plight, portent, predicament, presage, quicksand,
   risk, rocks ahead, storm clouds, strait, thin ice, tip-off,
   ultimatum, verbum sapienti, warning, warning piece



Bouvier's Law Dictionary, Revised 6th Ed (1856):

THREAT, crim. law. A menace of destruction or injury to the lives or
property of those against whom it is made.
     2. Sending threatening letters to persons for the purpose of extorting
money, is said to, be a misdemeanor at common law. Hawk. B. 1, c. 53, s. 1;
2 Russ. on Cr. 575; 2 Chit. Cr. L. 841; 4 Bl. Com. l26. To be indictable,
the threat must be of a nature calculated to overcome a firm and prudent
man. The party who makes a threat may be held to bail for his good
behaviour. Vide Com. Dig. Battery, D;  13 Vin. Ab. 357.



Bouvier's Law Dictionary, Revised 6th Ed (1856):

THREAT, evidence. Menace.
     2. When a confession is obtained from a person accused of crime, in
consequence of a threat, evidence of such confession cannot be received,
because, being obtained by the torture of fear, it comes in so questionable
a shape, that no credit ought to be given to it; 1 Leach, 263; this is the
general principle, but what amounts to a threat is not so easily defined. It
is proper to observe, however, that the threat must be made by a person
having authority over the prisoner, or by another in the presence of such
authorized person, and not dissented from by the latter. 8 C. & P. 733. Vide
Confession, and the cases there cited.