The Collaborative International Dictionary of English v.0.48:

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

The Collaborative International Dictionary of English v.0.48:

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]

The Collaborative International Dictionary of English v.0.48:

Lye \Lye\, n. (Railroad)
   A short side line, connected with the main line; a turn-out;
   a siding. [Eng.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

lye
    n 1: a strong solution of sodium or potassium hydroxide