She is monophthongising the vowels in her speech.

The linguist monophthongised the vowel sounds in the speech sample.

She decided to monophthongise the word to make it easier to pronounce.

He monophthongises his vowels when he speaks.

Monophthongisation is the process of reducing a diphthong to a monophthong.

The monophthongisations in this dialect are fascinating.