tree (as opposed to shrub)
"The arbor provided shade over the garden path, unlike the nearby bushes that offered only partial cover."
A shady sitting place or pergola usually in a park or garden, surrounded by climbing shrubs, vines or other vegetation.
"The machinist carefully aligned the arbor to ensure the pulley rotated smoothly without wobble."
An axis or shaft supporting a rotating part on a lathe.
In plain English: An arbor is an outdoor garden structure with posts and overhead branches that provides shade but has no roof walls.
"The children played under the old arbor in the garden."
Usage: Use arbor to describe an open-sided structure covered with plants for shade and seating in gardens or parks. Do not confuse this outdoor feature with the mechanical shaft used to hold workpieces on a machine tool.
The word "arbor" comes from the Old French word erbier, which originally meant a field or kitchen garden. Its root is the Latin herba, meaning grass or herb, though the modern spelling was later influenced by the Latin word for tree.