1) Centennial 2) Hundred years 3) Hundredth anniversary 4) Infrequent observance 5) Period 6) Period of time 7) The 100th anniversary 8) Time period Found on https://www.crosswordclues.com/clue/centenary
• (a.) Relating to, or consisting of, a hundred. • (a.) Occurring once in every hundred years; centennial. • (n.) A commemoration or celebration of an event which occurred a hundred years before. • (n.) The aggregate of a hundred single things; specifically, a century. Found on http://thinkexist.com/dictionary/meaning/centenary/
[Noun] Plural form: centenaries. A 100 years after an important event. Example: The college celebrated its centenary 100 years after it had opened.
Found on http://www.bbc.co.uk/skillswise/glossary/
Cen'te·na·ry adjective [ Latin centenarius , from centum a hundred.] 1. Relating to, or consisting of, a hundred. 2. Occurring once in every hundred years; centennial. ' Centenary solemnities.' Fuller. Found on http://www.encyclo.co.uk/webster/C/44