octennial

• POS: Adjective
• HYPHEN: oc=ten=ni=al

CIDE DICTIONARY

octennial, a. [L. octennium a period of eight years; octo eight + annus year.].

 Happening every eighth year; also, lasting a period of eight years.  [1913 Webster]

OXFORD DICTIONARY

octennial, adj.
1 lasting eight years.
2 occurring every eight years.

Etymology

LL octennium period of eight years (as OCT-, annus year)