failure to develop; absence.

failure of an organ or part to develop (for instance, eyelid agenesis)

Absence of part(s) of the body.

Incomplete or imperfect development.

Lack of development of something. For example, agenesis of a toe means that toe failed to form

absence, failure of formation or imperfect development of any part.

Imperfect development or lack of development.

Agenesis is the medical term for the failure of an organ to develop during embrionic growth and development. Agenesis of key organs such as the heart and brain is usually fatal. However, for those organs which occur in pairs, the loss of one member (i.e. "unilateral agenisis") is not.