The Collaborative International Dictionary of English v.0.48:

Neoplasm \Ne"o*plasm\ (n[=e]"[-o]*pl[a^]z'm), n. [See
   Neoplasia.] (Physiol. & Med.)
   A new formation or tissue, the product of morbid action.
   [1913 Webster]

WordNet (r) 3.0 (2006):

neoplasm
    n 1: an abnormal new mass of tissue that serves no purpose [syn:
         tumor, tumour, neoplasm]