[lye] n [ME, fr. OE leag; akin to OHG louga lye, L lavare, lavere to wash, Gk louein] (bef. 12c) 1: a strong alkaline liquor rich in potassium carbonate leached from wood ashes and used esp. in making soap and washing; broadly: a strong alkaline solution (as of sodium hydroxide or potassium hydroxide)
2: a solid caustic (as sodium hydroxide)