duodecennial

From Latin duodecennium (“12-year period”) + English -al (“forming adjs”), equivalent to borrowing the unattested duodecennialis.

• (General American) IPA^(key): /ˌduːoʊdɪˈsɛnɪəl/
• (Received Pronunciation) IPA^(key): /ˌdjuːəʊdɪˈsɛnɪəl/

duodecennial (not comparable)

1. Consisting of twelve years, occurring in 12-year cycles.

   The duodecennial Chinese zodiac originated from Chinese and Indian observations of the duodecennial cycle of the Jovian orbit.

2. Occurring once a duodecade, occurring every 12 years.

   The concept of a duodecennial "Jupiter return" in Western astrology arose from similar concerns.

• “duodecennial, adj.”, in OED Online ⁠, Oxford: Oxford University Press, 2018.