sex·cen·te·nar·y 
(sĕk-sĕntə-nĕr′ē, sĕk′sĕn-tĕnə-rē)
(sĕk-sĕntə-nĕr′ē, sĕk′sĕn-tĕnə-rē)adj.
Relating to 600 or to a 600-year period.
n. pl. sex·cen·te·nar·ies
A 600th anniversary or its commemoration.
[From Latin sexcentēnī, six hundred each : sex, six; see SEX- + centēnī, a hundred each (from centum, hundred; see dek in the Appendix of Indo-European roots).]