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Webster 1913 Edition

Adj.

[L.

octennium

a period of eight years;

octo

eight +

annus

year.]

Happening every eighth year; also, lasting a period of eight years.

Johnson.

–

Oc-ten′ni-al-ly

adv.

Adj.

[L. octo, eight, and annus, year.]

Happening every eighth year.

Lasting eight years.

octennial ‎(not comparable)