quaternary ammonium compound

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of a group of compounds composed of a cation, in which a central nitrogen atom is joined to four organic groups, and any of various anions, used as antiseptics, solvents, and emulsifying agents.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun chemistry An amine derivative, containing four radicals, of general formula R1R2R3R4-N+X-; the radicals may be the same, different, or part of a ring; X is any univalent anion such as OH-.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a compound derived from ammonium with hydrogen atoms replaced by organic groups; used as surface-active agents, disinfectants, and in drugs