All 4 Uses of

arbor
in
Arrowsmith

It was a wooden house with towers, swings, hammocks, rather mussy shade trees, a rather mangy lawn, a rather damp arbor, and an old carriage-house with a line of steel spikes along the ridge pole.
Chpt 19 *

arbor = a framework that supports climbing plants; or a shady rest area made by such a framework or by trees and shrubs

The seedy Pickerbaugh domain was enchanted; the tangled grass was a garden of roses, the ragged grape-arbor a shrine to Diana, the old hammock turned to fringed cloth of silver, the bad-tempered and sputtering lawn-sprinkler a fountain, and over all the world was the proper witchery of moonstruck love.
Chpt 21

Uses with a meaning too rare to warrant foucs:

At the hospital, the hall-man cried, "Shooting case in the Arbor, Doc."
Chpt 11 *

arbor = the name of a place

The Doctor, and The Doctor alone, was safe by night in the slum called "the Arbor."
Chpt 11

Definitions:

(1) (arbor as in: shaded arbor)
a framework that supports climbing plants; or a shady rest area made by such a framework or by trees and shrubs

The framework of an arbor is generally thought of as a wood lattice made to support vines, but it can also be a natural framework such as trees.
(2) (meaning too rare to warrant focus)
meaning too rare to warrant focus:

Much more rarely, an arbor can be used as a proper noun to reference a location. As a common noun, it can also reference various types of rotating machine shafts.