rickettsia n.

word-forming element in names of countries, diseases, and flowers, from Latin and Greek -ia, noun ending, in Greek especially used in forming abstract nouns (typically of feminine gender); see -a (1). The classical suffix in its usual evolution (via French -ie) comes to Modern English as -y (as in familia/family, also -logy, -graphy). Compare -cy.

In paraphernalia, Mammalia, regalia, etc. it represents Latin or Greek -a (see -a (2)), plural suffix of nouns in -ium (Latin) or -ion (Greek), with formative or euphonic -i-.

disease caused by vitamin D deficiency, 1630s, of uncertain origin (see note in OED). Originally a local name for the disease in Dorset and Somerset, England. Some derive it from a Dorset word, rucket "to breathe with difficulty," but the sense connection is difficult. The Modern Latin name for the disease, rachitis, comes from Greek rhakhis "spine" (see rachitic), but this was chosen by English physician Daniel Whistler (1619-1684) for resemblance to rickets.

masc. proper name, Middle English Rycharde, from Old French Richard, from Old High German Ricohard "strong in rule," from Proto-Germanic *rik- "ruler" (see rich) + *harthu "hard," from PIE *kar-o- (from PIE root *kar- "hard"). "One of the most popular names introduced by the Normans. Usually Latinized as Ricardus, the common form was Ricard, whence the pet form Rick, etc." ["Dictionary of English Surnames"]