Source : Webster's Revised Unabridged Dictionary (1913)

Agenesis \A*gen"e*sis\, n. [Gr. 'a priv. + ? birth.] (Physiol.)
   Any imperfect development of the body, or any anomaly of
   organization.

Source : WordNet®

agenesis
     n : imperfect development; nondevelopment of a part [syn: {agenesia}]