Plain English Meaning
A compound is a substance made when two or more elements join chemically to form something new. Once joined, the parts cannot be pulled apart by simply mixing or filtering -- it takes a chemical change to break them up.
Full Definition
Substances made by chemically combining two or more elements in fixed proportions, producing a new material whose properties differ from those of the elements that formed it. The atoms in a compound are bonded together and cannot be separated by physical means -- only by chemical reaction.
Context Anchor
Seen in aviation maintenance and aircraft systems discussions involving fuel, batteries, corrosion, cleaners, and materials.
Derivation
From Latin componere, meaning 'to put together.' A compound is literally something 'put together' from parts -- in chemistry, from elements that have bonded into a new substance.
Why Pilots Care
Pilots and mechanics may need to recognize that a compound can behave differently from the materials that formed it, especially in fuel contamination, corrosion, fumes, and aircraft-approved cleaning products.
Intuition Check
Do not read compounds here as just “several things placed together.” In this technical sense, compounds are substances whose parts are chemically joined into a new material.
Example Sentence 1
Water and carbon dioxide are compounds produced when aviation fuel burns in the engine.
Example Sentence 2
Only FAA-approved corrosion preventive compounds may be applied to the landing gear struts during the annual inspection.