The phrase "only event" is an idiomatic expression that means something happened only once, or it was a unique occurrence. It can also imply that what occurred was the most important thing to happen at the time and nothing else mattered.
Sentences with «only event»
It isn't only events in your childhood that can cause it. (eddinscounseling.com)
The purchase party remains one of the most well attended — and arguably most entertaining — members - only events of the year, and the recent gathering proved no exception. (palmermuseum.psu.edu)
There will also be invite - only events for global brands. (scamalytics.com)