Fennel flowers. Fennel (Foeniculum vulgare) is a herb with a variety of industrial, medicinal and culinary uses. As a medicinal herb, 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.