Source : Webster's Revised Unabridged Dictionary (1913)

Arrant \Ar"rant\, a. [OE. erraunt, errant, errand, equiv. to E.
   errant wandering, which was first applied to vagabonds, as an
   errant rogue, an errant thief, and hence passed gradually
   into its present and worse sense. See {Errant}.]
   Notoriously or pre["e]minently bad; thorough or downright, in
   a bad sense; shameless; unmitigated; as, an arrant rogue or
   coward.

         I discover an arrant laziness in my soul. --Fuller.

   2. Thorough or downright, in a good sense. [Obs.]

            An arrant honest woman.               --Burton.

Source : WordNet®

arrant
     adj : without qualification; used informally as (often pejorative)
           intensifiers; "an arrant fool"; "a complete coward"; "a
           consummate fool"; "a double-dyed villain"; "gross
           negligence"; "a perfect idiot"; "pure folly"; "what a
           sodding mess"; "stark staring mad"; "a thoroughgoing
           villain"; "utter nonsense" [syn: {arrant(a)}, {complete(a)},
            {consummate(a)}, {double-dyed(a)}, {everlasting(a)}, {gross(a)},
            {perfect(a)}, {pure(a)}, {sodding(a)}, {stark(a)}, {staring(a)},
            {thoroughgoing(a)}, {utter(a)}]