Lye (?), n. [Written also lie and ley.] [AS. leáh; 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]

Lye, n. A falsehood. [Obs.] See Lie.
[1913 Webster]