Centennial is a see also of centenary. As adjectives the difference between centennial and centenary is that centennial is relating to, or associated with, the commemoration of an event that happened a hundred years before while centenary is of, pertaining to, or completing a period of 100 years. As nouns the difference between centennial and centenary is that centennial is the hundredth anniversary of an event or happening while centenary is a one hundredth anniversary.