Fennel is a greyish-green, strong-smelling herbaceous perennial, with slim stems, bearing soft lacy, dark green leaves with thread-like lobes and swollen bases. Creeping rootstock gradually extends plant into a sparse clump. Reaching a height of 1.5 meters, the plant has small mustard-yellow flowers on a compound umbel. The fruit splits into two seeds, which are oval in shape with five ridges. The seed is light green to gray, about 0.75 cm long, and curved.

The seeds are used for scenting soaps and perfumes and for flavoring candies, liqueurs, medicines, and foods, particularly pastry, sweet pickles, and fish. Fennel is generally used as a condiment and culinary spice in food and beverages. It is used in some curry powder mixes. Toasting Fennel Seeds accentuates their flavor. It is also known to have medicinal properties.

As a medicinal plant, fennel seed has been used as an antispasmodic, carminative, diuretic, expectorant, laxative, stimulant, and stomachic. Roots once boiled as a vegetable, and used as an expectorant in cough mixtures. Fennel has also been used to stimulate lactation, as a remedy against colic, and to improve the taste of other medicines. Chinese herbal medicine includes the use of fennel for gastroenteritis, hernia, indigestion, abdominal pain, and to resolve phlegm and stimulate milk production. Fennel is known to provoke both photodermatitis and contact dermatitis in humans. The volatile oil may cause nausea, vomiting, seizures, and pulmonary edema. The essential oil has been reported to stimulate liver regeneration in rats. It has antibacterial properties.