Fronting (phonetics)

In phonology, fronting is a sound change in which a vowel or consonant becomes fronted, advanced or pronounced farther to the front of the vocal tract than some reference point. Fronting may be triggered by a nearby sound, in which case it is a form of assimilation, or may occur on its own. In general, a front vowel is pronouned in the front of the vocal tract.

In i-mutation and Germanic umlaut, a back vowel is fronted because of a following /i/ or /j/. This is assimilation.

In many dialects of English, the vowel /uː/ is fronted to [u̟ː] or [ʉː]. This sound change also occurred in many dialects of Norwegian and Standard Swedish, but not in Danish.

In the Attic and Ionic dialects of Ancient Greek, Proto-Greek close back /u uː/ were fronted to /y yː/. This change occurred in all cases and was not triggered by a nearby front consonant or vowel.

In Old English and Old Frisian, the back vowels /ɑ ɑː/ were fronted to /æ æː/ in certain cases. For more information, see Phonological history of Old English §§ First a-fronting​ and Second a-fronting.

...
Wikipedia