Noun
1. A branch of biology that deals the study of the processes through which an organism forms, from zygote to full structure (dictionary.com)
2. The study of the physiological changes that occurs within individual organisms from their conception through reaching physical maturity. (wiktionary.com)
3. The study of the process by which organisms grow and develop. Modern developmental biology studies the genetic control of cell growth, differentiation and “morphogenesis”, which is the process that gives rise to tissues, organs and anatomy, and even regeneration and aging, more recently. (wikipedia.com)
4. The study of how a multicellular organism develops from its early immature forms (zygote, larva, embryo, etc.) into an adult. (biology-online.org)