Active Principle:  A plant chemical proven to have a medical effect.

Antiseptic:  A substance that prevents or stops the growth of microorganisms that cause infection.

Astringent:  A substance the draws together the soft tissues such as skin or mucous membranes.

Decoction:  A drink or liquid extract made by boiling plant bark, roots, berries, or seeds in water.

Diuretic:  A substance that increases the flow of urine.

Emollient:  A substance that softens and soothes the skin and mucous membranes.

Essential Oil:  A plant oil that vaporizes readily and is often obtained by steam distillation.

Expectorant:  A substance that loosens and helps to expel phlegm.

Herbal Tea:  A beverage made from steeping or boiling herbs.

Infusion:  A preparation in which flowers, leaves, or stems are steeped in water that is not boiling.

Liquid extract:  Concentrated infusion made by soaking an herb in distilled water, grain alcohol, or glycerin for a long period.

Mucous membrane:  Lining of the body passage, such as the throat, that protects itself with secretions of mucus.

Photosensitivity:  Sensitivity to sunlight, resulting in a rash or burning sensation, brought on by ingestion or application of certain substances.

Plaster:  Gauze or cloth in which medicine has been wrapped.  Plaster is typically applied to the skin.

Poultice:  An herbal preparation that is usually applied directly to the affected area to relieve pain or swelling.

Purgative:  A very strong laxative.

Tannins:  Astringent and bitter compounds found in the seeds and skins of grapes, which slow oxidation and aging.

Tincture:  An herbal liquid extract that generally involves macerating the herb in alcohol.

Volatile Oil:  A plant oil that vaporizes readily and is often obtained by steam distillation, used interchangeably with essential oil.

Wash:  A liquid herbal medicine preparation for external use.