The Collaborative International Dictionary of English v.0.48:

Err \Err\ ([~e]r), v. i. [imp. & p. p. Erred; p. pr. & vb. n.
   Erring (?; 277, 85).] [F. errer, L. errare; akin to G.
   irren, OHG. irran, v. t., irr[=o]n, v. i., OS. irrien, Sw.
   irra, Dan. irre, Goth, a['i]rzjan to lead astray, airzise
   astray.]
   1. To wander; to roam; to stray. [Archaic] "Why wilt thou err
      from me?" --Keble.
      [1913 Webster]

            What seemeth to you, if there were to a man an
            hundred sheep and one of them hath erred. --Wyclif
                                                  (Matt. xviii.
                                                  12).
      [1913 Webster]

   2. To deviate from the true course; to miss the thing aimed
      at. "My jealous aim might err." --Shak.
      [1913 Webster]

   3. To miss intellectual truth; to fall into error; to mistake
      in judgment or opinion; to be mistaken.
      [1913 Webster]

            The man may err in his judgment of circumstances.
                                                  --Tillotson.
      [1913 Webster]

   4. To deviate morally from the right way; to go astray, in a
      figurative sense; to do wrong; to sin.
      [1913 Webster]

            Do they not err that devise evil?     --Prov. xiv.
                                                  22.
      [1913 Webster]

   5. To offend, as by erring.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

erring \erring\ adj.
   capable of making an error.

   Syn: errant, error-prone.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

erring
    adj 1: capable of making an error; "all men are error-prone"
           [syn: erring, error-prone]