[1880–85; tri- + centennial]This word is first recorded in the period 1880–85. Other words that entered Englishat around the same time include: Chief of Staff, automatism, impressionism, irredentist, rain checktri- is a combining form meaning “three,” used in the formation of compound words. Otherwords that use the affix tri- include: trigeminal, triglyceride, trilemma, trinomial, trivial