A monophthong is a pure vowel sound. The monophthongs can be contrasted with diphthongs, where the vowel quality changes within the same syllable, and hiatus, where two vowels are next to each other in different syllables. While "pure" vowels, or monophthongs, are said to have one target articulator position, diphthongs have two, and triphthongs three. http://en.wikipedia.org/wiki/Monophthong
Do all the varieties of spoken English in the UK have the same number of monophthongs ? What about in the U.S.?