Crossword clues for crottal crottal Any of several lichens of the genus Parmelia from which reddish brown or purple dyes are made The Collaborative International Dictionary crottal crottal \crottal\ n. any of several lichens of the genus Parmelia from which reddish brown or purple dyes are made. [Also spelled crottle and crotal.]Syn: . WordNet crottal n. any of several lichens of the genus Parmelia from which reddish brown or purple dyes are made [syn: crottle, crotal]