Lye is a caustic solution which is made from hard wood ashes and is used for glassmaking, soap making, textile production, biodiesel processing, and certain food preparations. In food use, some examples include: lutefisk, table olives, and Chinese preserved duck eggs (also known as "hundred-year-old eggs" or century eggs) Lye may also refer to:
- Soda lye—known as sodium hydroxide.
- Potash lye—a less common name for potassium hydroxide.
- Chamber lye—urine.