1. A shelter of trees or vines:
* Open space: A place without any trees or vines for shade.
* Clearing: An open area in a forest.
* Desert: A barren landscape devoid of trees.
* Plain: A flat area without trees or significant elevation changes.
* Building: A man-made structure used for shelter.
2. A structure supporting vines:
* Wall: A vertical structure without any vines.
* Fence: A barrier without any vines.
* Trellis: A structure supporting vines but usually with a more geometric design.
* Pergola: A structure with a roof, typically used for shade.
The best antonym for "arbor" depends on the specific context in which it is used.