In plural: a mixture of salts, including chlorides and sulphates of sodium, potassium, and magnesium, found associated with rock salt at Stassfurt, Germany. In singular: any such salt; such salts collectively.
Late 19th century; earliest use found in William Crookes (1832–1919), chemist and science journalist. From German Abraumsalz, lit. ‘salts to be removed’ (so named because they were formerly considered useless; from Abraum overburden, specifically use (in mining terminology) of Abraum refuse, trash, lit. ‘objects which need to be taken away’ (1399 as aberüm; from abraumen to take away, clear out (now abräumen; Middle High German abraumen) from ab- + raumen (now räumen) to empty, to vacate) + Salz), with substitution of salt for the second element.