Triennial

a.	1.	Continuing three years; as, triennial parliaments; a triennial reign.
	2.	Happening, coming about, or appearing once in every three years; as, triennial elections; a triennial catalogue; a triennial visitation.
n.	1.	Something which takes place or appears once in three years.

Noun	1.	triennial - the 300th anniversary (or the celebration of it) Synonyms: tercentenary, tercentennial
Adj.	1.	triennial - occurring every third year or lasting 3 years

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