Essential Oil
Essential oils are known also as volatile oils and are found in many plants. Some examples of essential oils are absinthol, benzaldehyde, borneol and camphor.
Essential oils evaporate easily and are usually responsible for the odor of plants. It is a category encompassing a wide variety of compounds, including alcohols, phenols and acids.
Essential oils have a large range of biological activities. For example, absinthol is toxic, while benzaldehyde has antispasmodic and anesthetic qualities.
References
Leung, Albert Y. 1980. Encyclopedia of Common Natural Ingredient used in Food, Drugs and Cosmetics. John Wiley and Sons, N Y. 409 pp.