Real Dictionary

Great Vowel Shift in British English
the complex series of sound developments ( c. 1400 to c. 1750) which changed the vowel system of Middle English into that of Modern English: Middle English long high vowels ( (i) and ; u) ) changed to Modern English diphthongs (; aɪ) and ; aʊ) ), and long
noun: a phonetic change that took place during the transition from Middle to Modern English, whereby the long vowels were raised (eː became iː , oː became uː , etc). The vowels (iː ) and (uː ) underwent breaking and became the diphthongs (aɪ ) and (aʊ )
noun: a series of changes in the quality of the long vowels between Middle and Modern English as a result of which all were raised, while the high vowels (i) and (uː), already at the upper limit, underwent breaking to become the diphthongs (ai) and (au)