centennial vs centenary

centennial and centenary both are nouns.

Word	Noun	Adjective	Verb	Adverb
centennial	Yes	Yes	No	No
centenary	Yes	Yes	No	No

As adjectives, centennial and centenary are synonyms defined as:

centennial and centenary: of or relating to or completing a period of 100 years

As nouns, centennial and centenary are synonyms defined as:

centennial and centenary: the 100th anniversary (or the celebration of it)

centennial (noun)	centenary (noun)
the 100th anniversary (or the celebration of it)	the 100th anniversary (or the celebration of it)

centennial (adjective)	centenary (adjective)
of or relating to or completing a period of 100 years	of or relating to or completing a period of 100 years