The Collaborative International Dictionary of English v.0.48:

Ontogenesis \On`to*gen"e*sis\, Ontogeny \On*tog"e*ny\, n. [See
   Ontology, and Genesis.] (Biol.)
   The history of the individual development of an organism; the
   sequence of events involved in the development of an
   organism; the history of the evolution of the germ; the
   development of an individual organism, -- in distinction from
   phylogeny, or evolution of the tribe. Called also
   henogenesis, henogeny.

   Syn: growth, growing, maturation, development.
        [1913 Webster]

WordNet (r) 3.0 (2006):

ontogeny
    n 1: (biology) the process of an individual organism growing
         organically; a purely biological unfolding of events
         involved in an organism changing gradually from a simple to
         a more complex level; "he proposed an indicator of osseous
         development in children" [syn: growth, growing,
         maturation, development, ontogeny, ontogenesis]
         [ant: nondevelopment]