dipolar ion

[dī-pōlər]
n.
  1. An ion having both a negative and a positive charge, each localized at a different point in the molecule, which thus has both positive and negative poles.zwitterion
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.