pathology 1. the establishment of a food relationship between a microscopic organism, pathogen, or parasitic plant, and a host 2. the whole pathogenic organism or parasitic plant and associated host symptoms, e.g., a limb rust organism and associated gall, the aerial shoots and endophytic system of a dwarf mistletoe and associated host swelling —see endophyte, infestationThis definition last updated 10/29/2008