Definition of "facade"

In Egypt the façades of their rock-cut tombs were […] ornamented so simply and unobtrusively as rather to belie than to announce their internal magnificence.

1865, James Fergusson, A History of Architecture in All Countries

Like so many of the finest churches, [the cathedral of Siena] was furnished with a plain substantial front wall, intended to serve as the backing and support of an ornamental façade.

1880, Charles Eliot Norton, Historical Studies of Church-Building in the Middle Ages

The house of Ruthven was a small but ultra-modern limestone affair, between Madison and Fifth ; […]. As a matter of fact its narrow ornate façade presented not a single quiet space that the eyes might rest on after a tiring attempt to follow and codify the arabesques, foliations, and intricate vermiculations of what some disrespectfully dubbed as “near-aissance.”

1907 August, Robert W[illiam] Chambers, chapter V, in The Younger Set, New York, N.Y.: D. Appleton & Company

Eight or so gunmen stood shoulder to shoulder in the gray-white trail before the barn, firing into the saloon's burning, bullet-pocked facade.

2005, Peter Brandvold, “Ghost Colts”, in Robert J. Randisi, editor, Lone Star Law‎, Simon and Schuster, page 179

Facades are widely used for tasks like simplifying complex APIs.

2017, Evan Burchard, Refactoring JavaScript: Turning Bad Code Into Good Code, O'Reilly Media, page 311