1. (Science: botany) A perennial, cruciferous plant (Cheiranthus Cheiri), with sweet-scented flowers varying in colour from yellow to orange and deep red. In Europe it very common on old walls.
The name is sometimes extended to other species of Cheiranthus and of the related genus Erysimum, especially the American western wallflower (Erysimum asperum), a biennial herb with orange-yellow flowers.
2. A lady at a ball, who, either from choice, or because not asked to dance, remains a spectator.