metastasis

A change in nature, form, or quality.

(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.

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

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