IPA: //kwəˈdrɛn.i.əl//
KK: /kwɑˈdrɛn.i.əl/
Something that happens or lasts for four years.
The quadrennial event attracts participants from all over the world.
Quadrennial → It is formed from "quad-" (meaning four) and "annus" (meaning year). The word "quadrennial" refers to an event that occurs every four years.
Think of 'four' ('quad-') and 'year' ('annus') to remember that 'quadrennial' means something that happens every four years.
No commonly confused words.