(1) A term in the classification of lip position in phonetics, referring to the visual appearance of the lips when they are held fairly close together and stretched sideways, as in a slightly open smile. Spread lips are noticeable in close vowels, as in the [i] of see, and contrast with neutral, open and rounded lip positions.
(2) In some models of non-linear phonology, spreading refers to the association (or linking) of a feature or node belonging to one segment with an adjacent segment; the disassociation of a feature or node from a segment is called delinking. The notion is of particular importance in the study of assimilation, where the effect of spreading produces an output representation with multilinked nodes, and dissimilation, where a feature or node is delinked from a segment, and the orphaned node is later deleted.
(3) In autosegmental phonology, spreading refers to a type of rule which extends the association of a tone in a given direction. Spreading is indicated by an arrow in the autosegmental rule, pointing to the right for unbounded rightward spreading, and to the left for unbounded leftward spreading.