1731, from M.L. rotarius "pertaining to wheels," from L. rota "wheel," from PIE base *roto- "to run, to turn, to roll" (cf. Skt. rathah "car, chariot;" Avestan ratho; Lith. ratas "wheel," ritu "I roll;" O.H.G. rad, Ger. Rad, Du. rad, O.Fris. reth, O.S. rath, O.Ir. roth, Welsh rhod "carriage wheel"). The international service club (founded by Paul P. Harris in Chicago in 1905) so called from the practice of clubs entertaining in rotation. Hence Rotarian (1911).