-enni-, -ennial, -ennium

(Latin: year, years)

quinquennially
quinquennium (s), quinquennia (pl)
A period of five years.
semicentennial
septenary, septennary (adjectives)
1. That which is lasting for seven years.
2. Occurring every seven years.
septennate (s), septennates (pl) (nouns)
A period of seven years.
septennial
septennially
septennium (s), sepennia (pl) (nouns)
A cycle or unit of time equal to seven years.
septicentennial
sesquicentennial (adjective) (not comparable)
Referring to a period of 150 years or pertaining to something that occurs every 150 years; relating to or happening after a period of 150 years.
sexennial
sexennially
sexennium
tercentennial
1. A 300th anniversary or its celebration.
2. The three-hundredth anniversary of an event; tricentennial. 2006 was the tercentennial of Benajmin Franklin's birth.
tricennial
1. Pertaining to thirty years.
2. Consisting of thirty years.
3. Occurring once in every thirty years.
4. Etymology: from Latin tricennium, "thirty years"; from triginta "thirty" + annus, "year" (tricennalis).