root beer

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

• noun A carbonated soft drink flavored with extracts of certain plant roots and herbs and usually artificial flavorings.

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

• noun A beverage, most often a carbonated soft drink made from a combination of vanilla, cherry tree bark, licorice root, sarsaparilla root, sassafras root bark, nutmeg, anise, and molasses among other things.

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

• noun carbonated drink containing extracts of roots and herbs