centenary (adj.)

1640s, "relation to or consisting of 100 years," from Latin centenarius "of a hundred, relating to a hundred," from centenai "a hundred each," from centum "hundred" (see hundred).

As a noun, c. 1600 as "period of 100 years;" 1788 as "a hundredth anniversary, commemoration or celebration of a hundredth anniversary." The usual British word in this sense for the American centennial.