<p><strong>Noun</strong></p><ul><li>A person who, because of shyness, unpopularity, or lack of a partner, remains at the side at a party or dance.</li><li>Any person, organization, etc., that remains on or has been forced to the sidelines of any activity: <em>The firm was a wallflower in this year's bidding for government contracts.</em></li><li>A European plant, <em>Cheiranthus cheiri</em>, 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.</li><li>Any of several related plants of the genera <em>Cheiranthus</em> and <em>Erysimum</em>.</li></ul>