"Ozarks" is a toponym believed derived as a linguistic corruption of "aux Arkansas" in the decades prior to the French and Indian War. Eventually, the term came to refer to all Ozark Plateau drainage into the Arkansas and Missouri Rivers.
Other possible derivations include "aux arcs" meaning "toward the arches" in reference to the dozens of natural bridges formed by erosion and collapsed caves in the Ozark region. These include Clifty Hollow Natural Bridge (actually a series of arches) in Missouri, and Alum Cove in the Ozark-St. Francis National Forest. It is even suggested "aux arcs" is an abbreviation of "aux arcs-en-ciel", French for "toward the rainbows" which are a common sight in the mountainous regions. After the Louisiana Purchase, American travelers in the region referred to various features of the upland areas using the term "Ozark", such as "Ozark Mountains" and "Ozark forests." By the early 20th century, "The Ozarks" had become a generic term. |source|