The Collaborative International Dictionary of English v.0.48:

amphoteric \am`pho*ter"ic\ ([a^]m`f[-o]*t[e^]r"[i^]k), a. [Gr.
   'amfo`teros both.]
   1. Partly one and partly the other
      [1913 Webster]

   2. Especially: (Chem.) Having both acidic and basic groups
      within the same molecule, and consequently neither acid
      nor alkaline; neutral. [R.] --Smart.
      [PJC] amphotericin

WordNet (r) 3.0 (2006):

amphoteric
    adj 1: having characteristics of both an acid and a base and
           capable of reacting as either [syn: amphoteric,
           amphiprotic] [ant: acidic, alkalic, alkaline]