ac·ti·no·ba·cil·lus \-_bəˈsiləs\noun Etymology: New Latin, from actin- + bacillus 1.capitalized: a genus of aerobic gram-negative parasitic bacteria (family Brucellaceae) forming filaments resembling streptobacilli — see actinobacillosis 2.pluralactinobacil·li\-iˌlī\: a bacterium of the genus Actinobacillus