A few Basic Terms

Aromatic =   having a distinct scent that is usually pleasing and may be herbaceous or spicy

Essential Oil =  An aromatic oil distilled from a plant.  These are volatile oils - they evaporate easily and quickly.  They also tend to have low flash points which is why products like diffuser blends must ship by ground only.

Carrier Oil =  Carrier oils are the 'fixed' oils and butters - they don't evaporate.  These oils are more stable than essential oils and have long chains of fatty acids.  They can be used in cooking and for topical application.  Many of them also have their own therapeutic properties which may contribute benefits to a blend.  They are referred to as carrier oils because they 'carry' the essential oils into your skin.  Flash points for carrier oils tend to be very high, so blends with carrier oils can ship faster.
It's important to note here that carrier oils can be blended without EOs to use on your skin. This comes in handy when someone should not be using essential oils (like a woman who is pregnant, or a young baby).    Example:  My Skin Butter: SMS is made with Shea Butter, Mango Butter, and Safflower Oil, with Arrowroot Powder added to improve the whipped texture.  This blend can be safely used on all ages from newborn to 100 + and has been great on diaper rash and rough, dry skin.

Chemical Constituents = The individual chemicals found in a substance. 
In aromatherapy, they are the individual chemicals that are found in essential oils and hydrosols.  They may be referred to as CTs. 
Example:  You have an EO called 'Thyme ct thymol' (Latin name:  Thymus vulgaris ct thymol.  This means you have Thyme essential oil with a high level of a chemical constituent called thymol.

Contact Dermatitis = swelling of the skin that is the result of a substance coming into contact with the skin.  It may appear as raised bumps or a rash.

Diffusion =  spreading a substance.  In aromatherapy, aromas are spread in the air via a special diffuser (NOT a humidifier) in a room or a car, or diffuser jewelry for a more personal level.

Diluted = to make thinner or weaker.  In aromatherapy, diluting an essential oil means adding it to a carrier oil so that the essential oil is a small percentage of the solution.

Flash Point = the lowest temperature at which the vapor of a volatile substance will burst into flame when exposed to a condition like fire or sparks or high heat.  

​Hydrosol =  Many aromatic plants go through a water distillation process to extract the essential oils.  The water used during distillation soaks up some of the chemical constituents  from the plant material.  The water then has an aroma and may have very mild therapeutic properties.  Hydrosols are generally considered safe for all ages and are great to use with infants.

Ingestion = taking a substance into the body

Mitigate = to make less serious or severe

Neat = without dilution

Orifice Reducer Cap = is a small, plastic part that fits into the opening of a bottle and provides a small opening that allows liquid to pass through drop by drop.  

Oxidized = oxygen molecules attach to other chemical molecules.  When that happens, the original chemical structure changes.  If an essential oil oxidizes, it can irritate the skin.  When a carrier oil oxidizes, we say it goes rancid.  In both cases, the aroma of the oil will change.  That aromatic change is much easier to detect with a carrier oil.

Topical Use = used on the surface of the skin

Volatile = evaporates quickly and easily