Diacs, or diacritical marks, are symbols, such as an accent (´) or cedilla (ç), which are placed above or below a letter in a written word to indicate a special pronunciation or a different meaning. Diacritical marks are often used to differentiate between homonyms and to show which syllable of a multi-syllable word should be emphasized. They are also used in many languages to indicate proper grammar, such as a noun being in a plural form or a verb in its past tense. Diacs can also be used to indicate tones in languages like Vietnamese and Chinese.