Definition of Rochelle salt in US English:

Rochelle salt

noun

  • The crystalline salt potassium sodium tartrate tetrahydrate, used as a reagent in various processes (e.g. silvering mirrors), as a pressure-sensitive material in transducers (because of the crystals' strongly piezoelectric properties), and formerly as a laxative.

Origin

Late 16th century; earliest use found in Edinburgh Testaments.