diagonal rib
A projecting rib that crosses a square or rectangular rib vault from corner to corner.

See also: RibIllustrated Dictionary of Architecture Copyright © 2012, 2002, 1998 by The McGraw-Hill Companies, Inc. All rights reserved
diagonal rib
A rib crossing a bay or compartment of a vault on a diagonal.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.