"Pharmacognosy" derives from two Greek words, "pharmakon" or drug, and "gnosis" or knowledge. While representing a classical field of science, Pharmacognosy has undergone significant change in recent years and today represents a highly interdisciplinary science which is one of five major areas of pharmaceutical education.
Its scope includes the study of the physical, chemical, biochemical and biological properties of drugs, drug substances, or potential drugs or drug substances of natural origin as well as the search for new drugs from natural sources. Research problems in pharmacognosy include studies in the areas of phytochemistry, microbial chemistry, biosynthesis, biotransformation, chemotaxonomy, and other biological and chemical sciences.
For an extended definition and overview, see Wikipedia - Pharmacognosy.