Source : Webster's Revised Unabridged Dictionary (1913)

Impetuous \Im*pet"u*ous\, a. [F. impetueux, L. impetuosus. See
   {Impetus}.]
   1. Rushing with force and violence; moving with impetus;
      furious; forcible; violent; as, an impetuous wind; an
      impetuous torrent.

            Went pouring forward with impetuous speed. --Byron.

   2. Vehement in feeling; hasty; passionate; violent; as, a man
      of impetuous temper.

            The people, on their holidays, Impetuous, insolent,
            unquenchable.                         --Milton.

   Syn: Forcible; rapid; hasty; precipitate; furious;
        boisterous; violent; raging; fierce; passionate. --
        {Im*pet"u*ous*ly}, adv. -- {Im*pet"u*ous*ness}, n.

Source : WordNet®

impetuousness
     n : rash impulsiveness [syn: {impetuosity}]