That separates or distinguishes; -- applied to points or marks used to distinguish letters of similar form, or different sounds of the same letter, as, a, ã, ä, o, o, etc.
A small mark (such as an accent mark) added above, below, before, or after a base character to modify its pronunciation or significance.
A sign, usually small, placed above, below or across a letter or group of letters in order to change the phonemic value of the original letter(s), or to denote stress or tone, or to distinguish between two words. Examples: German , , ; š and _ in the romanization of Russian Cyrillic; in the romanization of Hebrew; Polish _; Romanian _; French (where) as against ou (or). See also marker.