"urine used as a detergent," 1570s, from chamber (n.) in the "privy" sense + lye.
Entries linking to chamber-lye
chamber n.
c. 1200, "a room in a house," usually a private one, from Old French chambre "room, chamber, apartment" (11c.), from Late Latin camera "a chamber, room" (see camera).
The Old French word and the Middle English one also were used alone and in combinations to form words for "latrine, privy" from the notion of "bedroom utensil for containing urine." In anatomy, "enclosed space in a body," from late 14c. Of machinery, "artificial cavity," from 1769.
The gunnery sense of "part of the bore in which the charge is placed" is from 1620s. The meaning "legislative body" is from c. 1400, an extended sense from the chambers or rooms where an assembly meets. Chamber music (1765) traditionally was that meant to be performed in smaller spaces.
DA CAMERA: of the chamber, i. e. belonging to the chamber, suitable for the chamber, designed for the chamber,—a term applied to parlor or chamber music. [Godfrey Weber's General Music Teacher," Boston, 1842]
lye n.
Old English læg, leag "lye, water impregnated with alkaline salt absorbed from the ashes of wood by leaching," from Proto-Germanic *laugo (source also of Middle Dutch loghe, Dutch loog, Old High German louga, German Lauge "lye"), from PIE root *leue- "to wash."
The substance formerly was used in place of soap, hence Old High German luhhen "to wash," Old Norse laug "hot bath, hot spring," Danish lørdag, Swedish lördag "Saturday," literally "washing-day," "the day appropriated by the Scandinavians to that exercise" [Century Dictionary]. Chamber-lye in early Modern English was the name for urine used as a detergent.