[adj] not forming a syllable or the nucleus of a syllable; (of a consonant sound) accompanied in the same syllable by a vowel sound as the `n' in `botany' when pronounced `botny'; (of a vowel sound) dominated by other vowel sounds in a syllable; i.e. being the second vowel in a falling diphthong as the `i' in `oi'
UNSYLLABIC is a 10 letter word that starts with U.
WordNet Dictionary