A term used by some intonation analysts, particularly those working within the British tradition, to refer to a distinctive sequence of pitches, or tones, in an utterance; also called a tone group. The essential feature of a tone unit is the nuclear tone, the most prominent tone in the sequence; and this may be accompanied, depending on the length of the utterance, by other components, such as the head (i.e. the sequence of syllables between the first stressed syllable and the nuclear tone), pre-head (i.e. unstressed syllables at the very beginning of the tone unit) and tail (i.e. the syllables following the nuclear tone). A tone unit usually corresponds to a clause or sentence, but may be used on any grammatical unit.