Lye \Lye\, n. [Written also {lie} and {ley}.] [AS. le['a]h; akin to D. loog, OHG. louga, G. lauge; cf. Icel. laug a bath, a hot spring.] 1. A strong caustic alkaline solution of potassium salts, obtained by leaching wood ashes. It is much used in making soap, etc. [1913 Webster] 2. (Chem.) Sodium hydroxide or potassium hydroxide, or a concentrated aqueous solution of either compound. [PJC]