Name an ingredient that gives a drink a floral flavor.

Elderflower liqueur is a well-known ingredient that imparts a distinct floral flavor to cocktails. This liqueur is often made from elderflower blossoms, which have a delicate perfume and sweetness that can enhance a drink's overall profile. Its unique taste promotes a refreshing and aromatic quality, making it popular in various drinks, such as spritzers and other cocktails that seek to add an elegant floral note.

Other herbs, like rosemary, basil, and thyme, while they may have aromatic qualities and contribute various flavor dimensions to cocktails, do not inherently provide a floral flavor in the same way elderflower liqueur does. Rosemary offers a more piney and herbal taste, basil adds a sweet, peppery note, and thyme has earthy and slightly minty undertones. However, none of these options evoke the specific floral essence that elderflower liqueur does, reinforcing why it stands out as the correct answer.