The Century Dictionary and Cyclopedia defines [Singular](http://www.micmap.org/dicfro/previous/century-dictionary/5648/7/singular) as meaning:

> 7. Out of the usual course; unusual, uncomon; somewhat strange; a little extraordinary: As a singlular phenomena

More literally it derives from single, meaning one, so a singular phenomena is logistically something that is assessed as happening just once. It is of course possible to use the term hyperbolicly or mistakenly, which can diminish the effect, but I doubt you will find any word that lacks that particular problem. The nature of hyperbole is that people tend to exaggerate, and sometimes intentionally, so they will choose whichever word most effectively achieves the exaggeration they want to convey.

Since the dictionary entry was written, [Singular Event actually overtook singular phenomena in popularity](https://books.google.com/ngrams/graph?content=singular+event%2Csingular+phenomena&year_start=1800&year_end=2008&corpus=15&smoothing=3&share=&direct_url=t1%3B%2Csingular%20event%3B%2Cc0%3B.t1%3B%2Csingular%20phenomena%3B%2Cc0#t1%3B%2Csingular%20event%3B%2Cc0%3B.t1%3B%2Csingular%20phenomena%3B%2Cc0) as shown by google Ngrams, and collins shows that [singular](https://www.collinsdictionary.com/dictionary/english/singular) is one of the top 10,000 words used in the language, so I figure that this demonstrates that it is more than common and easily enough understood.

![This chart demonstrates the popularity of singular event vs singular phenomena. Both were very popular in the 1820s but declined usage until the 1940s, but afterwards singular event began to rise in popularity again while phenomona remained stable, making Singular event the more popular form by a few times over.](https://books.google.com/ngrams/chart?content=singular+event%2Csingular+phenomena&year_start=1800&year_end=2008&corpus=15&smoothing=3&share=&direct_url=t1%3B%2Csingular%20event%3B%2Cc0%3B.t1%3B%2Csingular%20phenomena%3B%2Cc0#t1%3B%2Csingular%20event%3B%2Cc0%3B.t1%3B%2Csingular%20phenomena%3B%2Cc0.png)