1. [adj]  not bearing a stress or accent; "short vowels are unstressed"
2. [adj]  used of vowels or syllables; pronounced with little or no stress; "a syllable that ends in a short vowel is a light syllable"; "a weak stress on the second syllable"
3. [adj]  used of syllables; "an atonic syllable carries no stress"

UNACCENTED is a 10 letter word that starts with U.