crottal vs crotal

crottal and crotal both are nouns.

Word	Noun	Adjective	Verb	Adverb
crottal	Yes	No	No	No
crotal	Yes	No	No	No

As nouns, crottal and crotal are synonyms defined as:

crottal and crotal: any of several lichens of the genus Parmelia from which reddish brown or purple dyes are made

Other synonyms of crottal include crottle.

crottal (noun)	crotal (noun)
any of several lichens of the genus Parmelia from which reddish brown or purple dyes are made	any of several lichens of the genus Parmelia from which reddish brown or purple dyes are made