a volatile substance found in different parts of many plants, including trees, and generally consisting of mixtures of hydrocarbons (i.e., terpenes), alcohols, esters, aldehydes, and ketones (e.g., camphor) but sometimes homogeneous —note 1. essential oils are in part responsible for the odor of flowers, leaves, and wood, from which they can be obtained by extraction or steam distillation —note 2. some forest trees yield essential oils that are, or have been, important commercially, e.g., camphor, cinnamon, eucalyptus, sandalwood —see natural resin, pine oil, rosin, tung oil This definition last updated 07/31/2008