Fennel (Foeniculum vulgare) flowers. Fennel is a herb with a variety of industrial, medicinal and culinary uses. Medicinally, it can be used as a diuretic (increasing urine production) and an antispasmodic (preventing involuntary muscle spasms). Industrially, it is used in perfumes and drinks as a flavouring agent. It is also widely used in cookery for its flavour.