The Collaborative International Dictionary of English v.0.48:

anionic \anionic\ adj.
   1. having the character of an anion; negatively charged;
      containing anions; -- of atoms, molecules, and groups of
      atoms. Contrasted with cationic.
      [PJC]

   2. of or pertaining to anions. Contrasted with cationic
      [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

anionic \anionic\ n.
   1. a class of synthetic detergents in which the molecules do
      not ionize in aqueous solutions.

   Syn: anionic detergent, non-ionic detergent
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

anionic
    adj 1: of or relating to anions [ant: cationic]
    n 1: a class of synthetic detergents in which the molecules do
         not ionize in aqueous solutions [syn: anionic detergent,
         anionic, non-ionic detergent]