over a vowel indicates that it is long. Technically known as macron.
over a vowel indicates that it is short. Technically known as breve. (As macron=makron, neuter of the Greek adjective makros, long, so breve=breve, neuter of the Latin adjective brevis, short.)
indicates that the vowel is sometimes long, sometimes short.
indicates an acute accent, as in blasé
indicates a grave * accent, as in breve
indicates a circumflex accent, as in fête; in a French word an omitted s is implied. But this accent is also used by phoneticians to indicate certain sounds. In Ancient Greek, the accent or or, later, placed over long vowels, indicated a compound tone-a rising falling tone.
' the cedilla, under c, before a or o or u, indicates in French that it is pronounced as s, as in façade.
the umlaut or the umlaut sign, as in German ä, ö, ü, denotes a vowel resulting from umlaut, assimilation of one vowel by a succeeding vowel (Müller=Mueller, Göring=Goering). In English and French, ¨ shows that the second of two sequent vowels is to be pronounced, as in Boötes and coöperative, and it is then named the diaeresis or, by some Americans, dieresis.
the tilde, belongs to Spanish and Portuguese; in the former it indicates a palatal nasal sound, as in cañon, anglicized as canyon, and in the latter that a tilde-surmounted vowel is pronounced nasally, as in João.
over c especially, but also over s and r, shows that č is pronounced tch, as in Čapek (tchapek). This Slavic, especially Czech, accent
aspirates the consonant. It is sometimes called 'a wing'. through a vowel, or over one, indicates, in Scandinavian languages, a sort of umlaut (compare the already mentioned ¨); the former accent occurs, for instance, in the Danish place-names Birkered and Kobenhavn (Copenhagen), and at least one printer calls it 'a bar-o'. The accent in å is, in colloquial reference by Danes, called 'a volle', literally a little round cake; å is also known as 'a Swedish-or, a Norwegian-a'. †
In prosody, a stressed syllable is indicated by either an acute accent,
* In Italian a grave accent, as in facoltà, denotes that the syllable (-tà) is stressed.
† I owe much of the information about č, ø and å to Professor Clark.