Bible Dictionaries
Litmus

Webster's Dictionary

(n.) A dyestuff extracted from certain lichens (Roccella tinctoria, Lecanora tartarea, etc.), as a blue amorphous mass which consists of a compound of the alkaline carbonates with certain coloring matters related to orcin and orcein.

Bibliography Information
Webster, Noah. Entry for 'Litmus'. Noah Webster's American Dictionary. https://www.studylight.org/​dictionaries/​eng/​web/​l/litmus.html. 1828.