Definitions
Consonant - An alphabetic or phonetic element other than a vowel; an elementary sound of speech which in the formation of a syllable is combined with a vowel. Applied both to the sounds and to the letters.
Vowel - A sound produced by the vibrations of the vocal cords; a letter or character representing such a sound (as a, e, i, etc.).
‘A vowel may be defined as voice (voiced breath) modified by some definite configuration of the super-glottal passages, but without audible friction (which would make it into a consonant)’ (Sweet Primer of Phonetics, ed. 2, §32).
Diphthong - A union of two vowels pronounced in one syllable; the combination of a sonantal with a consonantal vowel.
Philology - Love of learning and literature; the branch of knowledge that deals with the historical, linguistic, interpretative, and critical aspects of literature; literary or classical scholarship. Now chiefly U.S.