The Collaborative International Dictionary of English v.0.48:

malignant melanoma \malignant melanoma\ n. (Med.),
   Any of several malignant neoplasms (usually of the skin)
   consisting of melanocytes; called also melanoma. It is
   classed as a type of skin cancer.
   [WordNet 1.5]

WordNet (r) 3.0 (2006):

malignant melanoma
    n 1: any of several malignant neoplasms (usually of the skin)
         consisting of melanocytes [syn: melanoma, malignant
         melanoma]