meningococcusPronunciation: /mɪˌnɪŋgəʊˈkɒkəs, -ˌnɪndʒəʊ-/Definition of meningococcus noun (plural meningococci /-ˈkɒk(s)ʌɪ, -ˈkɒk(s)iː/) a bacterium involved in some forms of meningitis and cerebrospinal infection. Neisseria meningitidis Derivatives meningococcal adjective Origin: late 19th century: from meninges + coccusmeningococcus in other Oxford dictionaries Definition of meningococcus in the US English dictionary