Source : Webster's Revised Unabridged Dictionary (1913)

Excrescent \Ex*cres"cent\, a. [L. excresens, -entis, p. pr. of
   excrescere to grow out; ex out + crescere to grow. See
   {Crescent}.]
   Growing out in an abnormal or morbid manner or as a
   superfluity.

         Expunge the whole, or lip the excrescent parts. --Pope.

   {Excrescent letter} (Philol.), a letter which has been added
      to a root; as, the d in alder (AS. alr) is an excrescent
      letter.

Source : WordNet®

excrescent
     adj : forming an outgrowth (usually an excessive outgrowth)