An arbor is a garden area made from trees, vines and climbing plants trained into sides and a roof, usually through the use of latticework. The American spelling is arbor, the Canadian and British spelling is arbour. Arbor comes from the fourteenth century word, herber, meaning herb garden. Arbor Day is a day designated to raise awareness about the importance of planting trees, it was first celebrated in 1872 in the state of Nebraska, in the United States.
Some words end in -or in American English and -our in British English. These words come from two languages, French words which end in -ur and Latin words which end in -or. After the Norman conquest of England, French spellings with endings of -our became preferred. In the United States, the 1828 Webster’s dictionary settled on the -or endings of such words, which perpetuated this type of spelling in the United States.