semimillennial means of or related to a 500th anniversary. Lexicurio rates it Sui generis — a strength score of 95 out of 100.
Etymology
From semi- + millennial.
adj
- Of or related to a 500th anniversary.“On the occasion of the semimillennial anniversary of Uppsala University, Twelfth Symphony by the romantic Swedish composer Allan PETTERSSON, entitled De Döda på Torget (The Dead in the Marketplace) for chorus and orchestra […] is performed for the first time by the Stockholm Philharmonic.”
noun
- A 500th anniversary.“At a casual glance [Karl] Jaspers’ words seem to deprecate research, strange doctrine to preach at the semimillennial of an institution of learning as distinguished as the University of Basel.”