A stair built around a well, leaving an open space.See also: Stair
Illustrated Dictionary of Architecture Copyright © 2012, 2002, 1998 by The McGraw-Hill Companies, Inc. All rights reserved
A spiral stair constructed around an open cylindrical space without a central post, in contrast to a solid-newel stair built around a post.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.