fixed oils (chem.), non-volatile, oily substances, as stearine and olein, which leave a permanent greasy stain, and which can not be distilled unchanged; -- distinguished from volatile or essential oils... see fixed
Fixed oils Definition from Encyclopedia Dictionaries & Glossaries
An oil is any neutral, nonpolar chemical substance, that is a viscous liquid at ambient temperatures, and is both hydrophobic (immiscible with water, literally "water fearing") and lipophilic (miscible with other oils, literally "fat loving"). Oils have a high carbon and hydrogen content and are usually flammable and slippery.
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In the most general sense, an oil is any liquid not miscible with water.