- any of a number of lichens (genera Roccella, Dendrographa, and Lecanora) yielding purple dyes
- any of these, including litmus
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- Any of several lichens, chiefly of the genera Roccella and Lecanora, from which a dye is obtained.
- The violet dyestuff obtained from any of these organisms.
Origin: Middle English orchell, ultimately from Old Catalan orxella, perhaps of Mozarabic origin.