IPA: /kwɪnˈkwɛn.i.əm/
KK: /kwɪnˈkwɛniəm/
A time span that lasts for five years.
The project is planned to be completed over a quinquennium.
Quinquennium is formed from "quinque" (meaning five) and "annus" (meaning year). The word refers to a period of five years.
Think of 'five' ('quinque') years ('annus') to remember that quinquennium means a five-year period.
No commonly confused words.