The Collaborative International Dictionary of English v.0.48:

Sonant \So"nant\, a. [L. sonans, -antis, p. pr. of sonare to
   sound. See Sound a noise.]
   1. Of or pertaining to sound; sounding.
      [1913 Webster]

   2. (Phonetics) Uttered, as an element of speech, with tone or
      proper vocal sound, as distinguished from mere breath
      sound; intonated; voiced; vocal; tonic; the opposite of
      nonvocal, or surd; -- said of the vowels, semivowels,
      liquids, and nasals, and particularly of the consonants b,
      d, g hard, v, etc., as compared with their cognates p, t,
      k, f, etc., which are called nonvocal, surd, or aspirate.
      -- n. A sonant letter.
      [1913 Webster]

WordNet (r) 3.0 (2006):

sonant
    adj 1: produced with vibration of the vocal cords; "a frequently
           voiced opinion"; "voiced consonants such as `b' and `g'
           and `z'"; [syn: voiced, sonant, soft] [ant: hard,
           surd, unvoiced, voiceless]
    n 1: a speech sound accompanied by sound from the vocal cords
         [syn: sonant, voiced sound]

Moby Thesaurus II by Grady Ward, 1.0:

130 Moby Thesaurus words for "sonant":
   accented, allophone, alveolar, apical, apico-alveolar,
   apico-dental, articulate, articulated, articulation, aspiration,
   assimilated, assimilation, back, barytone, bilabial, broad,
   cacuminal, central, cerebral, check, checked, close, consonant,
   consonantal, continuant, dental, diphthong, dissimilated,
   dissimilation, dorsal, epenthetic vowel, explosive, flat, front,
   glide, glossal, glottal, glottalization, guttural, hard, heavy,
   high, intonated, labial, labialization, labiodental, labiovelar,
   laryngeal, lateral, lax, light, lingual, liquid, low,
   manner of articulation, mid, modification, monophthong,
   monophthongal, morphophoneme, mute, muted, narrow, nasal,
   nasalized, occlusive, open, oral, oxytone, palatal, palatalized,
   parasitic vowel, peak, pharyngeal, pharyngealization,
   pharyngealized, phone, phoneme, phonemic, phonetic, phonic, pitch,
   pitched, plosive, posttonic, prothetic vowel, retroflex, rounded,
   segmental phoneme, semivowel, soft, sonority, speech sound, spoken,
   stop, stopped, stressed, strong, surd, syllabic, syllabic nucleus,
   syllabic peak, syllable, tense, thick, throaty, tonal, tonic,
   transition sound, triphthong, twangy, unaccented, unrounded,
   unstressed, velar, viva, vocable, vocal, vocalic, vocoid, voice,
   voiced, voiced sound, voiceless, voiceless sound, voicing, vowel,
   vowellike, weak, wide