WordNet (r) 3.0 (2006):

unstressed
    adj 1: not bearing a stress or accent; "short vowels are
           unstressed" [ant: accented, stressed]

Moby Thesaurus II by Grady Ward, 1.0:

87 Moby Thesaurus words for "unstressed":
   accented, alveolar, apical, apico-alveolar, apico-dental,
   articulated, assimilated, back, barytone, bilabial, broad,
   cacuminal, central, cerebral, checked, close, consonant,
   consonantal, continuant, dental, dissimilated, dorsal, flat, front,
   glide, glossal, glottal, guttural, hard, heavy, high, intonated,
   labial, labiodental, labiovelar, lateral, lax, light, lingual,
   liquid, low, mid, monophthongal, muted, narrow, nasal, nasalized,
   occlusive, open, oxytone, palatal, palatalized, pharyngeal,
   pharyngealized, phonemic, phonetic, phonic, pitch, pitched,
   posttonic, retroflex, rounded, semivowel, soft, sonant, stopped,
   stressed, strong, surd, syllabic, tense, thick, throaty, tonal,
   tonic, twangy, unaccented, unrounded, velar, vocalic, vocoid,
   voiced, voiceless, vowel, vowellike, weak, wide