sexennially

sex·en·ni·al

S0300600 (sĕk-sĕn′ē-əl)adj.1. Occurring every six years.2. Relating to or lasting six years.n. An event that occurs every six years.
[From Latin sexennium, of six years : sex, six; see sex- + annus, year; see at- in Indo-European roots.]
sex·en′ni·al·ly adv.