The Collaborative International Dictionary
Septuagesimal
Septuagesimal \Sep`tu*a*ges"i*mal\, a. Consisting of seventy days, years, etc.; reckoned by seventies.
Our abridged and septuagesimal age.
--Sir T.
Browne.
Wiktionary
septuagesimal
a. Consisting of seventy days, years, etc.; reckoned by seventies.