Essential oil: An oil derived from a natural substance, usually either for its healing properties or as a perfume. Some pharmaceuticals, and many over-the-counter or 'holistic' remedies, are based on or contain essential oils. For example, products containing camphor or eucalyptus essential oils can help relieve congestive coughs, and many essential oils are used in the practice of aromatherapy.
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Last Editorial Review: 6/9/2016