Pronunciation: (brā'king),[key] —n. Phonol. the change of a pure vowel to a diphthong, esp. in certain environments, as, in Old English, the change of a vowel to a diphthong under the influence of a following consonant or combination of consonants, as the change of -a- to -ea- and of -e- to -eo- before preconsonantal r or l and before h, as in earm “arm” developed from arm, and eorthe “earth” from erthe. Also called vowel fracture.