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Webster 1913 Edition

(pĕr-ĕn′nĭ-yy̆)

Noun.

[L.

perennitas

The quality of being perennial.

[R.]

Derham.

Noun.

[L. perennitas.] An enduring or continuing through the whole year without ceasing.

perennity ‎(usually uncountable, plural perennities)

The quality of being perennial.
(Can we find and add a quotation of Derham to this entry?)