1840-50; < Latin: period of three years, equivalent to trienn(is) pertaining to three years (tri-tri- + -enn-, combining form of annus year + -is adj. suffix) + -ium-ium
Examples from the web for triennium
Continuing education hours taken during one triennium may not be transferred to a subsequent triennium.
Continuing competency hours taken during one triennium may not be transferred to a subsequent triennium.