All 7 Uses

atrium
in
Allegiant
(Auto-generated)

I reach the end of one hallway and find myself in an atrium, surrounded by the smell of wet earth.†
p. 139.2
I find myself in the atrium garden again, and this time, light glows behind the windows.†
p. 332.7
Cara jogs into the atrium, her hair askew and floating over her forehead.†
p. 332.8
Tobias takes me to the atrium near the hotel dormitory, and we spend some time there, talking and kissing and pointing out the strangest plants.†
p. 430.5
I stand on the higher step in the atrium and he stands on the lower one, so we're on the same plane.†
p. 431.3 *
He kisses me again, softly, and then leaves the atrium.†
p. 432.9
Most of the time I can tell when people are lying, and this must be a lie, because Tris is still alive, her eyes bright and her cheeks flushed and her small body full of power and strength, standing in a shaft of light in the atrium.†
p. 490.1

Definitions:

(1) (atrium as in: atrium of the building)
a central open space in a building -- often a large skylit hall near the entrance

In ancient Roman houses and early Christian churches, an atrium was an open courtyard. In many modern buildings, it is an indoor space that may include plants, water features, and balconies or walkways to other rooms.
(2) (atrium as in: right atrium of the heart)
chamber from which blood enters the heart
(3) (meaning too rare to warrant focus)
Much less commonly, atrium can refer to anatomical structures other than the heart.