rounding (n.)

A term used in the classification of lip position in PHONETICS, referring to the visual appearance of the lips when they assume a rounded shape, as in the ‘close rounding’ of [u] and the more ‘open rounding’ of  . Each of the VOWEL positions on the CARDINAL VOWEL diagram has both a rounded and an unrounded form, e.g. [i] v. [y], [e] v. [ø]. Lip position is of particular PHONOLOGICAL significance in the analysis of VOWEL and SEMI-VOWEL qualities.

The opposition rounded/non-rounded has special status in Chomsky and Halle’s DISTINCTIVE FEATURE theory of PHONOLOGY, where it handles variations in PLACE OF ARTICULATION (CAVITY features), specifying lip position. ‘Rounded’ sounds are defined articulatorily, as those produced with a narrowing of the lips, as in [w], [u], etc. Its opposite is non-rounded, referring to sounds produced without any such narrowing, as in English FRONT VOWELS.