Source : Webster's Revised Unabridged Dictionary (1913)

Tumor \Tu"mor\, n. [L., fr. tumere to swell: cf. F. tume['u]r.
   See {Tumid}.]
   1. (Med.) A morbid swelling, prominence, or growth, on any
      part of the body; especially, a growth produced by
      deposition of new tissue; a neoplasm.

   2. Affected pomp; bombast; swelling words or expressions;
      false magnificence or sublimity. [R.]

            Better, however, to be a flippant, than, by a
            revolting form of tumor and perplexity, to lead men
            into habits of intellect such as result from the
            modern vice of English style.         --De Quincey.

   {Encysted tumor}, a tumor which is inclosed in a membrane
      called a cyst, connected with the surrounding parts by the
      neighboring cellular substance.

   {Fatty tumor}. See under {Fatty}.

   {Innocent tumor}, or {Benign tumor}, one which does not of
      itself threaten life, and does not usually tend to recur
      after extirpation.

   {Malignant tumor}, a tumor which tends continually to spread,
      to become generalized in different parts of the body, and
      to recur after extirpation, and which, if left to itself,
      causes death.

Source : WordNet®

malignant tumor
     n : a tumor that is malignant and tends to spread to other parts
         of the body [syn: {malignant neoplasm}, {metastatic tumor}]