zest

n. 1 piquancy; stimulating flavour or quality. 2 a keen enjoyment or interest. B (often foll. By for) relish. C gusto. 3 scraping of orange or lemon peel as flavouring.  zestful adj. Zestfully adv. [french]

n. A piece of orange or lemon peel, or the aromatic oil which may be squeezed from such peel, used to give flavor to liquor, etc.