quatercentenary
noun
qua·ter·cen·te·na·ry ˌkwä-tər-sen-ˈte-nə-rē 
-ˈsen-tə-ˌner-ē
-ˈsen-tə-ˌner-ē -sen-ˈtē-nə-rē
: a 400th anniversary or its celebration
Word History
Etymology
Latin quater four times + English centenary — more at quaternion
First Known Use
1883, in the meaning defined above