n. A large crater formed by a volcanic explosion or by collapse of the cone of a volcano.
The Century Dictionary and Cyclopedia
n. A large kettle or caldron; hence, in geology, an amphitheatrical depression in a volcanic formation.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
n. a large crater caused by the violent explosion of a volcano that collapses into a depression
Word Usage
"I believe it has its own atmosphere because it is built in what you call a caldera, but I may have picked that information up from like a Syfy TV movie about the Coming Global Superstorm, or invented it in my own mind."