The Collaborative International Dictionary of English v.0.48:

Assonant \As"so*nant\, a. [L. assonans, p. pr. of assonare to
   sound to, to correspond to in sound; ad + sonare to sound,
   sonus sound: cf. F. assonant. See Sound.]
   1. Having a resemblance of sounds.
      [1913 Webster]

   2. (Pros.) Pertaining to the peculiar species of rhyme called
      assonance; not consonant.
      [1913 Webster]

WordNet (r) 3.0 (2006):

assonant
    adj 1: having the same sound (especially the same vowel sound)
           occurring in successive stressed syllables; "note the
           assonant words and syllables in `tilting at windmills'"
    2: having the same vowel sound occurring with different
       consonants in successive words or stressed syllables

Moby Thesaurus II by Grady Ward, 1.0:

48 Moby Thesaurus words for "assonant":
   accordant, according, alliteral, alliterating, alliterative,
   assonantal, attuned, belabored, blended, blending, chanting,
   chiming, cliche-ridden, concordant, consonant, dingdong, harmonic,
   harmonious, harmonizing, harping, homophonic, humdrum, in accord,
   in chorus, in concert, in concord, in sync, in tune, in unison,
   jingle-jangle, jingling, jog-trot, labored, monodic, monophonic,
   monotone, monotonous, punning, rhymed, rhyming, singsong,
   symphonious, synchronized, synchronous, tedious, tuned, unisonant,
   unisonous