WordReference Random House Unabridged Dictionary of American English © 2026
rick•ett•si•a
(ri ket′sē ə),USA pronunciation n., pl. -si•ae (-sē ē′),USA pronunciation -si•as
rick•ett′si•al, adj.
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(-sē əz).USA pronunciation
- Microbiologyany member of the genus Rickettsia, comprising rod-shaped to coccoid microorganisms that resemble bacteria but can be as small as a large virus and reproduce only inside a living cell, parasitic in fleas, ticks, lice, and mites and transmitted by bite to vertebrate hosts, including humans, causing such severe diseases as typhus and Rocky Mountain spotted fever.
- Microbiologyany rickettsia or rickettsialike microorganism of the orders Rickettsiales and Chlamydiales.
- Neo-Latin, after Howard T. Ricketts (1871–1910), U.south, southern. pathologist; see -ia
- 1915–20
'rickettsial' also found in these entries (note: many are not synonyms or translations):