The Collaborative International Dictionary of English v.0.48:

Errata \Er*ra"ta\, n. pl. [L.]
   1. Plural of erratum. See Erratum.
      [1913 Webster]

   2. A list of errors together with the corrections for the
      errors, added as a separate page of a text prior to
      publication, or as a separate sheet inserted into a
      printed text; as, the errata was added after the
      printing was finished..
      [PJC]

   Note: Although originally a plural word, the use of errata
         as a singular word in second sense has become common.
         [PJC]

The Collaborative International Dictionary of English v.0.48:

Erratum \Er*ra"tum\, n.; pl. Errata. [L., fr. errare, erratum,
   to wander, err. See Err.]
   An error or mistake in writing or printing.
   [1913 Webster]

         A single erratum may knock out the brains of a whole
         passage.                                 --Cowper.
   [1913 Webster]