i in fit .
The word also refers to a letter representing such a sound ( a , e , i , o , u , and sometimes y ). In articulatory {{link=phonetics">phonetics (see articulation ), vowels are classified by tongue and lip position; for example, high vowels like the i in machine and the u in flute are both pronounced with the tongue arched high in the mouth, but in u the lips are also rounded. Single vowel sounds are monophthongs; two vowel sounds pronounced as one syllable, like the ou in round , are diphthongs.