oxalic (adj.)

1791, in oxalic acid, a violently poisonous substance found in many plants and used in dyeing, bleaching, and printing, from French oxalique (1787, Lavoisier), literally "of or pertaining to sorrel," from Latin oxalis "sorrel," from Greek oxalis, from oxys "sharp" (from PIE root *ak- "be sharp, rise (out) to a point, pierce"). So called because it occurs in sorrel and was first isolated from it.