Webster's English Dictionary

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rickettsia

ric.ket.tsia \rik-'et-se--*\ \-se--.e-, -.i-\ \-se--*l\ n or ric.ket.tsi.as 
   or ric.ket.tsi.ae [NL, genus of microorganisms, fr. Howard T. Ricketts 
   -1910 Am pathologi] pl st : any of a family (Rickettsiaceae) of pleomorphic 
   rod-shaped nonfilterable  microorganisms that cause various diseases (as 
   thyphus) - ric.ket.tsi.al aj