nosemaPronunciation: /nəʊˈsiːmə/Definition of nosema noun a spore-forming parasitic protozoan that chiefly affects insects. Genus Nosema, phylum Microspora, kingdom Protista: several species, in particular N. apis, which causes infectious dysentery ( nosema disease) in honeybees Origin:modern Latin, from Greek nosēma 'disease'nosema in other Oxford dictionaries Definition of nosema in the US English dictionary