Definition
Ethyl alcohol (ethanol) that has been made unfit for drinking by the addition of small amounts of toxic or unpalatable substances, while remaining usable as a solvent, fuel, or industrial chemical.
Plain English
Drinking alcohol that has had something nasty added to it so people won't drink it, but it still works fine for cleaning, dissolving, or burning.
Context Anchor
Seen in aircraft maintenance instructions, shop material lists, and cleaning procedures, rather than normal flight procedures.
Derivation
From the Latin de- ('remove') and natura ('nature' or 'natural state'). To 'denature' something is to take away its natural character — here, the ability to be safely consumed. Knowing this helps: the alcohol itself is unchanged chemically for industrial purposes; only its drinkability has been removed.
Why Pilots Care
Provides an effective, residue-free cleaning agent that avoids regulatory restrictions on beverage alcohol.
Intuition Check
Denatured does not mean diluted or safer. It means the alcohol has been deliberately changed so it is unsafe to drink, even though it may still burn easily and work as a cleaner.
Example Sentence 1
The mechanic wiped the magneto contacts clean with denatured alcohol before reassembly.
Example Sentence 2
Denatured alcohol is approved for cleaning pitot tubes during preflight inspections.