What's the "een" in Halloween?
1640s, "evergreen," formed in English from Latin perennis "lasting through the year (or years)," from per- "through" (see per) + annus "year" (see annual). Botanical sense of "Remaining alive through a number of years" is attested from 1670s; figurative meaning of "enduring, permanent" is from 1750. Related: Perennially. For vowel change, see biennial. The noun meaning "a perennial plant" is from 1763.
Adjective Living for three or more years.
Noun A perennial plant. Herbaceous perennials survive winter and drought as underground roots, rhizomes, bulbs, corms, or tubers. Woody perennials, including vines, shrubs, and trees, usually stop growing during winter and drought. Asters, irises, tulips, and peonies are familiar garden perennials. Compare annual, biennial.