septennially
sep·ten·ni·al
(sĕp-tĕn′ē-əl)adj.
1. Occurring every seven years.
2. Consisting of or continuing for seven years.
n.
An event that occurs every seven years.
[From Late Latin septennium, period of seven years, from Latin septennis, of seven years : septem, seven; see septm̥ in Indo-European roots + annus, year; see at- in Indo-European roots.]
sep·ten′ni·al·ly adv.