The Collaborative International Dictionary of English v.0.48:

Ametabolic \A*met`a*bol"ic\, Ametabolous \Am`e*tab"o*lous\, a.
   (Zool.)
   Not undergoing any metamorphosis; as, ametabolic insects.
   Opposite of metabolic.
   [1913 Webster]

   2. undergoing only slight metamorphosis
      [WordNet 1.5]

WordNet (r) 3.0 (2006):

ametabolic
    adj 1: undergoing slight or no metamorphosis [syn: ametabolic,
           ametabolous] [ant: metabolic, metabolous]
    2: undergoing no (or only slight) metamorphosis