Origin: Latin suffix -ary
Centenary has 4 different meanings across 2 categories:
the 100th anniversary (or the celebration of it)
"The town hall was filled with pride as they unveiled a new fountain to mark the centenary of the library's opening."
Synonym of centennial: a hundredth anniversary.
"The town will hold a grand parade to celebrate its centenary next July."
Of, pertaining to, or completing a period of 100 years.
"The town hall is hosting a special gala to mark the centenary of its founding in 1924."