A diphthong is a gliding vowel sound normally represented by two adjacent vowels. In typography, some diphthongs are represented by a single ligature character (joined letters). The most commonly used diphthong ligatures are æ, oe, AE, and OE.
Intonation is the variation of tone used when speaking.
This can be used in various ways:
Intonation languages: languages that use pitch syntactically, for instance to convey surprise and irony or to change a sentence from a statement to a question. English is a well-known example.
Tonal languages: languages that use intonation to convey meaning, usually by using the pitch to make contrast between syllables. Thai is an example.
An intermediate position is occupied by languages with a melodic accent, for instance Swedish.
Rising intonation means the of the voice goes up; falling intonation means that the pitch goes down.
Speech sound produced by the vocal chords, formed into its
unique sound in the mouth and nowhere hindered in passage.
A vowel is of course also the character that represents such a sound.
The vowel letters are usually a, e, i, o, u and in some languages y (as in English) and w (as in Welsh).
All languages have at least two vowels and all languages contain the vowel a.