perennial

adj

1. (not-comparable)Lasting or remaining active throughout the year, for multiple years, or all the time.

   “a perennial stream”

   “[W]hat is most admirable is the vast enclosure, and variety of ground, in yᵉ large garden, containing vineyards, cornefields, meadows, groves (whereof one is of perennial greens), and walkes of vast lengthes, so accurately kept and cultivated, that nothing can be more agreeable.”

   “And there is ſuch a thing as Subterraneous Heat, […] [a]s is manifeſt from the ſmoking of perennial Fountains in froſty VVeather, and VVater dravvn out of Pumps and open VVells.”

   “It [the pond] is a clear and deep green well, half a mile long and a mile and three quarters in circumference, and contains about sixty-one and a half acres; a perennial spring in the midst of pine and oak woods, without any visible inlet or outlet except by the clouds and evaporation.”

   “That desert's age the gorge may prove, / Piercing profound the mountain bare; / Yet hardly churned out in the groove / By a perennial wear and tear / Of floods; nay, dry it shows within; / But twice a year the waters flow, / Nor then in tide, but dribbling thin: […]”

2. (figuratively, not-comparable)Continuing without cessation or intermission for several years, or for an undetermined or infinite period; never-ending or never failing; perpetual, unceasing.

   “His artwork has a perennial beauty.”

   “There, on perennial Adamant deſign'd, / The various Fortunes of your Race you'll find: […]”

   “Good humour may be defined a habit of being pleaſed, a conſtant and perennial ſoftneſs of manner, eaſineſs of approach, and ſuavity of diſpoſition; […]”

   “The perennial exiſtence of bodies corporate and their fortunes, are things particularly ſuited to a man who has long views; who meditates deſigns that require time in faſhioning; and which propoſe duration when they are accompliſhed.”

   “Has Ireland been governed in a 'wise and loving' manner? A government and guidance of white European men which has issued in perennial hunger of potatoes to the third man extant,—ought to drop a veil over its fact, and walk out of court under conduct of proper officers; saying no word; expecting now of a surety sentence either to change or die.”

3. (figuratively, not-comparable)Appearing or recurring again and again; recurrent.

   “a perennial candidate in elections”

   “Change is a perennial theme in politics.”

   “Ludgate Hill is not Moirosi’s Mountain, but, after all, is only a gentle ascent of about half an inch in the foot, over a length of about two hundred yards, up which unshod omnibus horses would trot with a full load in any weather. Yet there it must remain, a chief thoroughfare in the heart of London, a perennial cause of complaint, and of fear, disgust, and injury to man and horse.”

   “Of all the questions which, throughout the centuries, have escaped from the lips of man, there is none which has been asked with such persistence, none which has possessed interest more perennial, than "Whence do I come? Whither shall I go?" Man's origin, man's hereafter, have ever been of intensest interest to man.”

4. (figuratively, not-comparable, rare)Appearing or recurring again and again; recurrent.
5. (not-comparable)Of a plant: active throughout the year, or having a life cycle of more than two growing seasons.

noun

1. A plant that is active throughout the year, or has a life cycle of more than two growing seasons.

   “One would have supposed from the appearance of the country at the end of the first season after the eruption that practically all plants except the trees and bushes had been destroyed, and that revegetation must be due to new seedlings started on the ash. Such, however, is not the case. Excavation of the root systems of the new plants shows that they are old perennials which have come through the ash from the old soil.”

2. (broadly)A thing that lasts forever.
3. (broadly)A person or thing (such as a problem) that appears or returns regularly.

   “Some of the stars on our list are perennials who fill huge venues year after year after year, but there's also a returning superstar on our list of the hottest summer tours of 2019.”