The Collaborative International Dictionary of English v.0.48:

Onomatopoeic \On`o*mat`o*poe"ic\, a.
   Onomatopoetic. --Whitney.
   [1913 Webster]

WordNet (r) 3.0 (2006):

onomatopoeic
    adj 1: of or relating to or characterized by onomatopoeia [syn:
           onomatopoeic, onomatopoetic]
    2: (of words) formed in imitation of a natural sound;
       "onomatopoeic words are imitative of noises"; "it was
       independently developed in more than one place as an
       onomatopoetic term"- Harry Hoijer [syn: echoic,
       imitative, onomatopoeic, onomatopoeical,
       onomatopoetic] [ant: nonechoic]

Moby Thesaurus II by Grady Ward, 1.0:

40 Moby Thesaurus words for "onomatopoeic":
   apish, conjugate, delineatory, depictive, derivative, echoic,
   embodying, emulative, etymologic, figurative, graphic, ideographic,
   illustrational, illustrative, imitative, incarnating, lexical,
   lexicographic, lexicologic, lexigraphic, limning, mimetic, mimic,
   mimish, onomastic, onomatologic, onomatopoetic, paronymic,
   paronymous, personifying, pictographic, pictorial, portraying,
   representational, representative, representing, simulative,
   symbolizing, typifying, vivid