vancomycin Syllabification: (van·co·my·cin)Pronunciation: /ˌvaNGkəˈmīsin/Definition of vancomycin noun Medicine a bacterial antibiotic used against resistant strains of streptococcus and staphylococcus. This antibiotic is obtained from the bacterium Streptomyces orientalis Origin: 1950s: from vanco- (of unknown origin) + -mycinvancomycin in other Oxford dictionaries Definition of vancomycin in the British & World English dictionary