Real Dictionary

wallflower
countable noun: A wallflower is a plant that is grown in gardens and has sweet-smelling yellow, red, orange, or purple flowers.
countable noun: If you say that someone is a wallflower, you mean that they are shy and do not get involved in dancing or talking to people at social events.

wallflower in American English
any of a number of perennial or annual garden plants (genera Cheiranthus and Erysimum) of the crucifer family, having racemes of cross-shaped flowers, usually yellow or orange; esp., a common perennial ( C. cheiri) having racemes of fragrant, colorful flo
noun: a person who, because of shyness, unpopularity, or lack of a partner, remains at the side at a party or dance

wallflower in British English
noun: 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)