The Collaborative International Dictionary of English v.0.48:

Errant \Er"rant\, a. [F. errant, p. pr. fr. OF. errer to travel,
   LL. iterare, fr. L. iter journey; confused somewhat with L.
   errare to err. See Eyre, and cf. Arrant, Itinerant.]
   1. Wandering; deviating from an appointed course, or from a
      direct path; roving.
      [1913 Webster]

            Seven planets or errant stars in the lower orbs of
            heaven.                               --Sir T.
                                                  Browne.
      [1913 Webster]

   2. Notorious; notoriously bad; downright; arrant.
      [1913 Webster]

            Would make me an errant fool.         --B. Jonson.
      [1913 Webster]

   3. (Eng. Law) Journeying; itinerant; -- formerly applied to
      judges who went on circuit and to bailiffs at large.
      --Mozley & W.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Errant \Er"rant\, n.
   One who wanders about. [Obs.] --Fuller.
   [1913 Webster]

WordNet (r) 3.0 (2006):

errant
    adj 1: straying from the right course or from accepted
           standards; "errant youngsters"
    2: uncontrolled motion that is irregular or unpredictable; "an
       errant breeze"

Moby Thesaurus II by Grady Ward, 1.0:

114 Moby Thesaurus words for "errant":
   aberrant, aberrative, abroad, adrift, all abroad, all off,
   all wrong, amiss, askew, astray, at fault, awry, beside the mark,
   circuitous, circumforaneous, corrupt, deceptive, defective,
   delusive, departing, desultory, deviant, deviating, deviational,
   deviative, deviatory, devious, digressive, discursive, distorted,
   divagatory, drifting, errable, erratic, erring, erroneous,
   error-prone, excursive, fallacious, fallible, false, faultful,
   faulty, flawed, flitting, floating, footloose,
   footloose and fancy-free, fugitive, gadding, gypsy-like, gypsyish,
   heretical, heterodox, illogical, illusory, indirect, itinerant,
   labyrinthine, landloping, liable to error, mazy, meandering,
   migrational, migratory, misbehaving, mischievous, naughty, nomad,
   nomadic, not right, not true, off, off the track, open to error,
   out, out-of-the-way, peccant, perverse, perverted, planetary,
   rambling, ranging, roaming, roving, self-contradictory, serpentine,
   shifting, snaky, straggling, stray, straying, strolling, swerving,
   traipsing, transient, transitory, transmigratory, turning,
   twisting, undirected, unfactual, unorthodox, unproved, unreliable,
   untrue, vagabond, vagrant, veering, wandering, wide, winding,
   wrong, zigzag