amphoterism

[ăm′fə-tĕrĭz′əm, ăm-fŏtə-rĭz′əm]
n.
  1. The quality of exhibiting the characteristics of an acid and a base and having the capacity to react either as an acid or a base.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.