syllable, a segment of speech that consists of a vowel, with or without one or more accompanying consonant sounds immediately preceding or following—for example, a, I, out, too, cap, snap, check. A syllabic consonant, such as the final n sound in button and widen, also constitutes a syllable. Closed (checked) syllables are those that end in a consonant; open (free) syllables end in a vowel. The role that syllables play in the production of speech is a matter of considerable debate. So too is any more precise definition of the syllable in phonetics and phonology.