frosting

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

• noun Icing, as on a cake.
• noun A roughened or speckled surface imparted to glass or metal.

from The Century Dictionary.

• noun A composition generally made of confectioners' sugar mixed with whites of eggs, used to cover cake, etc.: so called from its white, frosty appearance.
• noun A dead or lusterless surface on metal, or a similar surface on any material, produced by etching or engraving, or by a punch or die.
• noun A material used for decorative work, as signs, etc., made from coarsely powdered thin flakes of glass: commonly in the plural.

from the GNU version of the Collaborative International Dictionary of English.

• noun A composition of sugar and beaten egg, used to cover or ornament cake, pudding, etc.
• noun A lusterless finish of metal or glass; the process of producing such a finish.
• noun the lightened color on part of an object, as of hair, produced by treatment with bleach or other chemicals; as only part of the object is thus treated, the final color of the object is two-toned; also, the process of producing such a two-toned effect.

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

• noun A sugary coating for cakes and other baked goods.
• noun A layer of frost.
• verb Present participle of to frost.

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

• noun a flavored sugar topping used to coat and decorate cakes