adv. [f. TRIENNIAL a. + -LY2.] Every three years; once in three years.
1689. in 6th Coll. Papers rel. Pres. Juncture, 25. The Parliament to be chosen Triennially, and to meet Annually.
1727. Bailey, vol. II., Triennially.
1806. W. Taylor, in Ann. Rev., IV. 714. It appears that the tithe ought to be levied triennially.
1881. Chamb. Jrnl., No. 914. 419/1. The gorgeous festival given triennially at the Crystal Palace.