IPA: //traɪˈɛn.ɪ.ə.li//
KK: /trɪˈɛnəli/
Happening every three years.
The conference is held triennially, bringing together experts from around the world.
Triennially → It is formed from "tri-" (meaning three) and "annus" (meaning year) combined with the suffix "-ly" (meaning in a manner). The word "triennially" means occurring every three years.
Think of 'three' ('tri-') and 'years' ('annus') to remember that 'triennially' refers to something that happens every three years.