noun
: any of a large class of volatile odoriferous oils of vegetable origin that impart to plants odor and often other characteristic properties, that are obtained from various parts of the plants (as flowers, leaves, or bark) by steam distillation, expression, or extraction, that are usually mixtures of compounds (as terpenoids, aldehydes, or esters), and that are used often in the form of essences in perfumes, flavoring materials, and pharmaceutical preparations — called also ethereal oil, volatile oil ; distinguished from fatty oil and fixed oil ; see oleoresin