A centenary is the hundredth anniversary of something. The centenary of the founding, a centenary edition, mark the centenary.
It is the British word; American English says centennial. The prefixes run in order — bicentenary for two hundred years, tercentenary for three. A centenarian is a person who has reached that age, which is a different word from the anniversary.
1nouncentenaryThe hundredth anniversary of something.
“The school celebrated its centenary with a party for everyone who had ever studied there.”
centenary is an anniversary.
Latin centenarius means containing a hundred, from centum, a hundred.
Latin
centēnārius
English, today
centenary
Built from
From Latin centēnārius. From Latin centēnārius (“containing 100; local official overseeing a hundred”), either directly or through French centenaire from centēnus (“100 each”) + -ārius, from centum (“hundred”). a doublet of centner and kantar and quintal.
Etymology from Wiktionary, CC BY-SA