Head to the Forest to Define Arboreal

Arbor, the Latin word for "tree," has been a rich source of tree-related words in English, though a few are fairly rare. Some arbor descendants are generally synonymous with arboreal: arboraceous, arborary, arboreous, and arborous. Others are primarily synonymous with arboreal in the sense of "relating to or resembling a tree": arborescent, arboresque, arborical, and arboriform. And one, arboricole, is a synonym of arboreal in its sense of "inhabiting trees." The verb arborize means "to branch freely," and arborvitae is the name of a shrub that means literally "tree of life." There's also arboretum, a place where trees are cultivated, and arboriculture, the cultivation of trees. And we can't forget Arbor Day, which since 1872 has named a day set aside by various states (and the national government) for planting trees. Despite its spelling, however, the English word arbor, in the sense of a "bower," does not have its roots in the Latin arbor. Instead, it arises by way of the Anglo-French herbe from the Latin herba, meaning "herb" or "grass."