novennium

Borrowed from Latin novennium (“9-year [period]”).

novennium (plural not attested)

1. (rare) A nine-year period or cycle.
   • 1871, Henry Scale English, Crowland and Burgh (volume 3, page 148)

     What he says of the novennium is an attempt at duplicity; he would have escaped with that if he could; he did not love to lie: What he says is that Ernulfus was a bishop a little over nine years […]

• (adj.): novennial
• (5-year period): quinquennium
• (6-year period): sexennium
• (7-year period): septennium, septenniad, septennary, septenary
• (8-year period): octennium
• (10-year period): decade