citric acid

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

• noun A colorless translucent crystalline acid, C₆H₈O₇, principally derived by fermentation of carbohydrates or from lemon, lime, and pineapple juices and used in preparing citrates and in flavorings and metal polishes.

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

• noun organic chemistry A colourless crystalline compound, 2-hydroxy-1,2,3-propanetricarboxylic acid, C6H8O7, found in citrous fruit; it is used as a food additive and in the manufacture of citrates.

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

• noun a weak water-soluble acid found in many fruits (especially citrus fruits); used as a flavoring agent