DECENNIAL Meaning of DECENNIAL in English [de.cen.ni.al] adj (ca. 1656) 1: consisting of or lasting for 10. years 2: occurring or being done every 10. years "the ~ census" -- decennial n -- de.cen.ni.al.ly adv Merriam-Webster English vocab. Английский словарь Merriam Webster. 2012