Definitions

I.consonant   
 
  
A basic speech sound in which the breath is at least partly obstructed and which can be combined with a vowel to form a syllable. 
 
(The Oxford Dictionary of English (revised edition). Ed. Catherine Soanes and Angus Stevenson. Oxford University Press, 2005. Oxford Reference Online. Oxford University Press.)
 
 
I.Vowel  

A speech sound which is produced by comparatively open configuration of the vocal tract, with vibration of the vocal cords but without audible friction, and which is a unit of the sound system of a language that forms the nucleus of a syllable. ...
(From The Oxford Dictionary of English (2nd edition revised) in English Dictionaries & Thesauruses)
   

 
II.Diphthong
 
(The Oxford Dictionary of English (revised edition). Ed. Catherine Soanes and Angus Stevenson. Oxford University Press, 2005)

A sound formed by the combination of two vowels in a single syllable, in which the sound begins as one vowel and moves towards another (as in coin, loud, and side). Often contrasted with monophthong, triphthong.