French purple

a dyestuff obtained from lichens and used for coloring woolen and silken fabrics, without the aid of mordants.
(Chem.) Same as Cudbear.

See also: French, Purple

Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.
References in periodicals archive ?
But a French purple patch that produced 13 points in just seven whirlwind minutes left Wales gasping and facing a huge second half mountain to climb.