abortifacient: Capable of inducing the abortion of a fetus.
absolute: A highly concentrated viscous liquid, solid, or semi-solid perfume product distilled from a concrete.
annual: A plant that completes its life cycle in one year.
aromatic extract: Products obtained by solvent extraction containing both volatile and non-volatile components.
axil: The area of a plant between a stem or branch and a leaf stem.
balsam: A naturally occurring mixture of resin and aromatic substances, which are usually acids.
balsamic: A strong scent, usually from an aromatic resin, that is often described as sweet, earthy, and rich.
basal leaves: Leaves that grow at the base of an upright stem and are different from the others that grow on the stem.
biennial: A plant that completes its life cycle in two years.
camphoraceous: A pungent, sharp scent resembling camphor.
carcinogenic: A substance that promotes cancer or cancerous growths.
carrier oil: An oil in which essential oils are diluted.
catkin: A thick, drooping cluster of tiny flowers.
chemotype: Variations in a plant species due to climate and location.
CO2 extraction: An extraction method, also called super-critical CO2 extraction, that uses liquid carbon dioxide to obtain aromatic material from plants.
cold-pressed: A mechanical method of oil extraction in which no external heat is used during the process. It is also known as expression.
compound leaf: A leaf comprised of small leaflets along a stem.
concrete: A highly concentrated solid or semi-solid waxy perfume product. It is used to make an absolute.
coniferous: A woody, usually evergreen, plant that reproduces through seed-bearing cones.
decoction: A preparation made by boiling plant material and reducing it to a concentration.
deciduous: A tree or woody plant that drops its leaves as part of an annual cycle.
diffuser: A device used to disperse fragrance into the air.
distillation: A method of extraction using steam or hot water to separate essential oil from plant material.
enfleurage: A time-consuming and labor-intensive method of extracting flower essence using a fatty substance such as tallow or lard.
essential oil: A volatile, aromatic liquid obtained through the processes of distillation and expression.
expression: A method of oil extraction, also called cold-pressing, in which no external heat is used during the process.
exudate: A natural material secreted by plants, which can be spontaneous or occur after damage to the plant.
fixative: An oil that slows the evaporation of volatile essential oils.
fixed oils: Oils obtained from plants that are fatty and non-volatile.
florets: Tiny, individual flowers that make up a larger flower head.
flower essence: An infusion of flowers in water which is then mixed in a 50% brandy solution. These are not essential oils.
flower head: A dense, compact cluster of tiny flowers.
flower water: A byproduct of distillation that contains the water-soluble molecules of aromatic plants. These are also called hydroflorates, hydrolats, and hydrosols.
fullers’ earth: Aluminum silicate used to remove as much color as possible from food-grade vegetable oils.
gum: A gel-like plant secretion that is water-soluble. This term often used in reference to resins, which are not water-soluble.
gum resin: A naturally occurring mixture of gum, resin, and a small amount of volatile oil.
heartwood: The centermost wood in a tree trunk.
herbaceous: An herbal scent, sometimes called a “green” fragrance.
hydro-diffusion: A distillation method of essential-oil extraction in which steam is forced into the vessel from above rather than below the plant material.
hydrosol: A water byproduct of distillation that contains the water-soluble molecules of aromatic plants. These are also called hydroflorates, hydrolats, and floral waters.
infusion: A mildly aromatic product created by steeping plant material in water or oil. This is also known as maceration.
kernel: The inner and softer part of a seed, nut, or fruit stone. In cereal plants, it is enclosed within a husk.
lipophilic: A property of essential oils that means they are readily absorbed by fatty oils and waxes. This property allows essential oils to be dispersed in carrier oils.
oleo gum resin: A naturally occurring mixture of gum, resin, and volatile oil.
oleoresin: A naturally occurring mixture of resin and volatile oil.
partially refined oil: An oil that has been put through processes that often include bleaching, deodorizing, and winterization to give it a longer shelf life.
perennial: A plant with a life cycle of more than two years.
photosensitivity: An effect, such as a rash or dark pigmentation of skin exposed to sunlight, that occurs within a few days after the use of some essential oils.
pomade: A perfumed fat obtained during the enfleurage extraction method.
refined oil: An oil, usually food-grade, produced to have no odor and very little to no color.
resin: A solid or semi-sold secretion from trees that is not water-soluble.
resin absolute: An absolute created from resin by a further extraction process using alcohol.
resinoid: A substance created by solvent extraction of resins, gums, balsams, oleo gum resins, or oleoresins. It can be a viscous liquid, a solid, or semi-solid.
rhizome: A stem that grows underground.
rosette: A description of leaves that grow closely together in a circle or spiral pattern.
sensitization: Unlike irritation, the skin becomes increasingly reactive or hypersensitive.
sepal: The outermost part of a flower that is usually green and functions to protect the young bud.
solvent extraction: A process that uses chemicals to obtain essential oil from plant material.
strewing herbs: It was a common practice in Europe to scatter certain herbs on floors to freshen the air, act as pest control, and make it easier to sweep away the detritus of everyday living.
strobile: A female catkin.
synergy: A harmony that results when the effect of a combination is greater than the sum of all it parts.
tincture: A plant extract prepared in an alcohol base.
toothed leaf: A leaf with serrated edges.
umbel: A description of an umbrella-like flower head structure.
unrefined oil: An oil that has not been put through various chemical processes to remove color, odor, and other natural properties.
virgin oil: Obtained from the first pressing of plant material.
volatile: A substance, such as an essential oil, that is unstable and evaporates rapidly.
water distillation: A method of extraction in which plant material is completely immersed in hot water.
whorl: A circular or spiral growth pattern of leaves, needles, or flower petals.