Anniversaries
Updated February 23, 2017 | Factmonster Staff 
The Question:
Is there a word that designates a 50th anniversary in the same way that sesquicentennial means a 150th?
The Answer:
Semicentennial generally denotes a 50th anniversary (or describes events or objects pertaining to it). A synonymous, though slightly less mellifluous, noun is quinquagenary.
Some other words along these lines are quinquennial (pertaining to a fifth anniversary, or a period of five years), quindecennial (15th aniversary), vigentennial (20th), and quasquicentennial (125th).
-The Fact Monster
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