Source : Webster's Revised Unabridged Dictionary (1913)

Indelible \In*del"i*ble\, a. [L. indelebilis; pref. in- not +
   delebilis capable of being destroyed: cf. F.
   ind['e]l['e]bile. See {In-} not, and {Deleble}.] [Formerly
   written also {indeleble}, which accords with the etymology of
   the word.]
   1. That can not be removed, washed away, blotted out, or
      effaced; incapable of being canceled, lost, or forgotten;
      as, indelible characters; an indelible stain; an indelible
      impression on the memory.

   2. That can not be annulled; indestructible. [R.]

            They are endued with indelible power from above.
                                                  --Sprat.

   {Indelible colors}, fast colors which do not fade or tarnish
      by exposure.

   {Indelible ink}, an ink obliterated by washing; esp., a
      solution of silver nitrate.

   Syn: Fixed; fast; permanent; ineffaceable. --
        {In*del"i*ble*ness}, n. -- {In*del"i*bly}, adv.

              Indelibly stamped and impressed.    --J. Ellis.

Source : WordNet®

indelible
     adj : cannot be removed, washed away or erased; "an indelible
           stain" [syn: {unerasable}]