a person who, because of shyness, unpopularity, or lack of a partner, remains at the side at a party or dance.
any person, organization, etc., that remains on or has been forced to the sidelines of any activity:
The firm was a wallflower in this year's bidding for government contracts.
a European plant, Cheiranthus cheiri, of the mustard family, that, when growing wild on walls, cliffs, etc., has sweet-scented, usually yellow or orange flowers, but when cultivated has flowers varying in color from pale yellow to brown-red or purple.
any of several related plants of the genera Cheiranthus and Erysimum.
Through good times and bad, it has remained a wallflower among meat cuts.
Island wallflower is also known to occur on public land.
Common wildflowers include wallflower, larkspur and penstemon.
Until now the country has been a wallflower and it is about time it put on its pumps.
Which isn't to say that a wallflower will necessarily remain a wallflower.
British Dictionary definitions for wallflower
Also called gillyflower. a plant, Cheiranthus cheiri, of S Europe, grown for its clusters of yellow, orange, brown, red, or purple fragrant flowers and naturalized on old walls, cliffs, etc: family Brassicaceae (crucifers)
any of numerous other crucifers of the genera Cheiranthus and Erysimum, having orange or yellow flowers
(informal) a person who stays on the fringes of a dance or party on account of lacking a partner or being shy