Definition of centennium in US English:

centennium

(also centenium)

noun

  • A period of a hundred years; a century. Also (occasionally): a celebration of the completion of a century; a centenary.

Origin

Early 19th century; earliest use found in Augustus Granville (1783–1872), physician and Italian patriot. From post-classical Latin centennium period of a hundred years from classical Latin centum hundred + -ennium (in biennium, triennium, etc.).