1. Circular window-aperture with spoke-like colonnettes or bars radiating from the centre, e.g. west front of Chartres Cathedral, France (late C12).
2. Circular part of an early Middle Pointed Geometrical window with bar-tracery.
"wheel-window." A Dictionary of Architecture and Landscape Architecture. . Encyclopedia.com. (August 21, 2018). http://www.encyclopedia.com/education/dictionaries-thesauruses-pictures-and-press-releases/wheel-window
"wheel-window." A Dictionary of Architecture and Landscape Architecture. . Retrieved August 21, 2018 from Encyclopedia.com: http://www.encyclopedia.com/education/dictionaries-thesauruses-pictures-and-press-releases/wheel-window