The British Marxist magazine The New Left Review announced recently it had reached its fiftieth anniversary. True to its uncompromising intellectuality, it referred to its “quinquagenary issue”.
Here’s another relatively recent sighting of this rare word:
Having dubbed himself variously as the Man Who Sold the World, the Man Who Fell to Earth, and now, simply, Earthling, David Bowie has more than just his quinquagenary to celebrate at Madison Square Garden January 9.
The New York Magazine, 13 Jan. 1997.
The term is from classical Latin quinquagenarius, consisting of fifty, or fifty years old. This has also given the English language quinquagenarian, a slightly better known term, whose adjectival senses overlap with those of quinquagenary, in particular one that refers to a person in their fifties.
By the way, if the journal survives a further quarter of a century, it will reach its semisesquicentennial. The prefix sesqui- is a shortened form of a Latin word meaning “a half in addition” or 1½ times; it appears in the rather better known sesquicentennial that refers to a a 150th anniversary. So semisesquicentennial refers to half of 1½ of 100 or 75. (If you prefer, you can replace semi- with either of the other prefixes meaning a half, demi- or hemi-. All are extremely rare.)
In a further fifty years, the magazine might celebrate its quasquicentennial (125th anniversary, a century plus a quarter, created irregularly from Latin roots in the early 1960s). Assuming a longevity that’s extremely rare in any publication, it might one day achieve its demisemiseptcentennial (its 175th anniversary, a half of a half of 700) and perhaps even its semiquincentennial (its 250th, half of 500).