Source : Webster's Revised Unabridged Dictionary (1913)

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.

         There is no terror, Cassius, in your threats. --Shak.

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

         Of all his threating reck not a mite.    --Chaucer.

         Our dreaded admiral from far they threat. --Dryden.

Source : WordNet®

threat
     n 1: something that is a source of danger; "earthquakes are a
          constant threat in Japan" [syn: {menace}]
     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}]