novocentenary

1. not comparableOf or relating to a 900th anniversary

   [...] the novocentenary year of the battle of Hastings; [...]

   1990, Archéologie médiévale, page x

plural novocentenaries

1. 900th anniversary

   [...] the novocentenary of the great Inquiry.

   1988, The Antiquaries Journal, page 361

   2 more examples

   [...] the novocentenary of the building of the Tower, Field Marshal Sir Geoffrey Baker, Constable of Her Majesty's Tower of London has directed that a pewter plate be cast, bearing the official emblem of the novocentenary.

   1978, Country Life, page 1371

   [...] the novocentenary of the Battle of Hastings, [...]

   1996, Château Gaillard, page 5