The American Heritage® Dictionary of the English Language, 4th Edition
adj. Diacritical.
adj. Medicine Diagnostic or distinctive.
n. A mark, such as the cedilla of façade or the acute accent of resumé, added to a letter to indicate a special phonetic value or distinguish words that are otherwise graphically identical.
adj. Denoting a distinguishing mark applied to a letter or character.
n. A special mark added to a letter to indicate a different pronunciation, stress, tone, or meaning.
the GNU version of the Collaborative International Dictionary of English
adj. That separates or distinguishes; -- applied to points or marks used to distinguish letters of similar form, or different sounds of the same letter, as, ā, ă, ä, ō, ŏ, etc.
The Century Dictionary and Cyclopedia
Serving to distinguish: same as diacritical (which is the more common form).
n. A diacritical mark (which see, under diacritical).
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
adj. capable of distinguishing
n. a mark added to a letter to indicate a special pronunciation
Word Usage
"AutoCorrect is programmed with a number of two - or three-key combinations that will correct the appearance of a letter with a diacritic."