Merriam-Webster's Word of the Day for April 24, 2026 is: arboreal \ahr-BOR-ee-ul\ adjective Arboreal is a formal and literary word used to describe something that relates to trees. It is also used in technical contexts to mean "living in or often found in trees," as in "arboreal primates." // Despite weekly hikes on the same trail, she never ceases to be amazed by the arboreal beauty. See the entry > Examples: "In the saplings' early years, slow growth is the key to arboreal longevity, so the matriarch keeps her offspring in the shade." — Mike Dilger, The Guardian (London), 21 Oct. 2025 Did you know? Arboreal took root in English in the 17th century, at a time when language influencers were eager to see English take on words from Latin and Greek. Apparently unsatisfied with a now-obsolete adjective treen meaning (as recorded in our Unabridged dictionary) "of, relating to, or derived from trees," they plucked arboreal from the Latin arboreus, meaning "of a tree"; its ultimate root is arbor, meaning "tree." That root arborized—that is, branched freely (to use the term figuratively): English abounds with largely obscure words that trace back to arbor, meaning "tree." Generally synonymous with arboreal are arboraceous, arborary, arboreous, and arborous. Synonymous with arboreal specifically in the sense of "relating to or resembling a tree" are arborescent, arboresque, arborical, and arboriform. Arboricole is a synonym of arboreal in its "inhabiting trees" sense. (The influencers may have overdone it a bit.) Arboreal is far more common than any of these, but other arbor words also have a firm hold in the language: arborvitae refers to a shrub whose name translates as "tree of life"; arboretum refers to a place where trees are cultivated; and arboriculture is the cultivation of trees. And of course we can't forget Arbor Day, which since 1872 has named a day set aside for planting trees. You'd be forgiven for assuming that the English word arbor, in the sense meaning "a garden shelter of tree boughs or vines twined together," is rooted in the same source as arboreal, but in fact it comes from the Latin noun herba, meaning "herb" or "grass."
