delabialize

verb (used with object), de·la·bi·al·ized, de·la·bi·al·iz·ing.

1. to deprive (a sound) of labial character, as in unrounding a vowel.

verb (used without object), de·la·bi·al·ized, de·la·bi·al·iz·ing.

2. (of a speech sound) to lose its labial character.