what is lye in soap
Medical Definition of LYE. 1. : a strong alkaline liquor rich in potassium carbonate leached from wood ashes and used especially in making soap and washing; broadly: a strong alkaline solution (as of sodium hydroxide or potassium hydroxide). 2.: a solid caustic (as sodium hydroxide).edical Definition of LYE. 1. : a strong alkaline liquor rich in potassium carbonate leached from wood ashes and used especially in making soap and washing; broadly: a strong alkaline solution (as of sodium hydroxide or potassium hydroxide). 2. : a solid caustic (as sodium hydroxide).