perennis

Perennial comes from Latin perennis, meaning 'lasting through the year,' from per- (through) and annus (year). In Latin, a fons perennis was a spring that flowed year-round, as opposed to a seasonal spring. The word described duration, not biology. English adopted it in the seventeenth century for plants that live for more than two growing seasons — perennial as opposed to annual (one year) or biennial (two years).

The botanical distinction matters. Annual plants germinate, flower, set seed, and die within a single growing season. Biennials take two years. Perennials persist — their root systems survive winter, and new growth emerges each spring. Herbaceous perennials die back to the ground but regrow from the roots. Woody perennials — trees and shrubs — keep their above-ground structure. The word perennial covers both, unified by the principle of persistence.

The figurative meaning appeared by the 1700s and may now be more common than the botanical one. A 'perennial problem' is one that recurs every year. A 'perennial favorite' is one that remains popular over time. A 'perennial candidate' runs for office repeatedly. The word communicates reliable return — something you can count on seeing again, whether or not you want to.

Horace used perennis in the Odes (~23 BCE): 'Exegi monumentum aere perennius' — 'I have built a monument more lasting than bronze.' The word was about permanence from the beginning. The plant meaning came later, but it fits: a perennial plant is one that has built a root system more lasting than a single season. The monument is underground.