1. The central roundel of a pattern or ornament.
2. The circular (or nearly circular) central part of a volute, as in an Ionic capital.
3. One of the smaller, more or less triangular, openings between the bars of Gothic tracery.
4. An oculus, esp. one at the summit of a dome.
5. A hole through material for access, to permit the passage of a pin, or to serve as a means of attachment.