crottle

 
Pronunciation: /ˈkrɒt(ə)l/
(also crotal)

noun

  • a common lichen found on rocks, used in Scotland to make a golden-brown or reddish-brown dye for staining wool for making tweed.
    • Parmelia saxatilis (order Parmeliales) and other species

Origin:

mid 18th century: from Scottish Gaelic and Irish crotal, crotan