sep·ten·ni·al 
(sĕp-tĕnē-əl)
(sĕp-tĕnē-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 sept in the Appendix of Indo-European roots + annus, year; see at- in the Appendix of Indo-European roots.]
sep·tenni·al·ly adv.
- Indo-European root: sperə-
- Indo-European root: spē-
- Indo-European root: sreu-
- Indo-European root: (s)teg-
- Indo-European root: stegh-
- Indo-European root: steig-
- Indo-European root: steigh-
- Indo-European root: stel-
- Indo-European root: (s)tenə-
- Indo-European root: ster-
- Indo-European root: ster-
- Indo-European root: ster-
- Indo-European root: streb(h)-
- Indo-European root: streig-
- Indo-European root: stā-
- Indo-European root: stāi-
- Indo-European root: s(w)e-
- Indo-European root: sweid-
- Indo-European root: s(w)eks
- Indo-European root: swel-
- Indo-European root: swen-
- Indo-European root: swep-
- Indo-European root: swer-
- Indo-European root: swesor-
- Indo-European root: swo-