rəˌketsēˈā(ˌ)lēz, (ˌ)riˌk- noun plural
Usage: capitalized
Etymology: New Latin, from Rickettsia + -ales
: an order of small pleomorphic gram-negative microorganisms of uncertain biological position that are obligate parasites living in vertebrates or in arthropods which often serve as vectors of those parasitic in vertebrates — see bartonellaceae , rickettsiaceae ; compare chlamydiaceae