Definition of "metastasis"

A change in nature, form, or quality.  examples

(medicine) The transference of a bodily function or disease to another part of the body, specifically the development of a secondary area of disease remote from the original site, as with some cancers.  quotations  examples

(figurative) The spread of a harmful event to another location, like the metastasis of a cancer.  examples

(rhetoric) Denying adversaries' arguments and turning the arguments back on them.  examples