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Webster 1913 Edition

Adj.

[L.

trietericus

, Gr. [GREEK], fr. [GREEK] (sc. [GREEK]) a triennial festival; [GREEK] (see

.) + [GREEK] a year.]

Kept or occurring once in three years; triennial.

[R.]

J. Gregory.

Adj.

[L. trietericus; tres, three, and Gr. year.]

Triennial; kept or occurring once in three years. [Little used.]

trieterical ‎(not comparable)

(rare) Triennial: occurring once in three years.
(Can we find and add a quotation of J. Gregory to this entry?)