What does litmus mean?
Litmus is a word with two linked lives: it names a blue coloring matter historically obtained from lichens and used to indicate whether a solution is acidic or alkaline, and it also names a decisive test of character, quality, or suitability. In scientific contexts, litmus paper or a litmus solution provides a simple chemical indicator, changing from red in acidic conditions to blue in alkaline conditions. In everyday and professional language, “the litmus test” means a practical criterion by which something can be judged. The expression often suggests that the chosen test is especially revealing: a résumé may be described as the litmus test for whether a candidate is organized and prepared. The word carries a generally neutral analytical tone, although it can imply that a test is decisive, discriminating, or even harsh. Litmus is consequently useful in both chemistry and figurative discussion, where it gives a vivid image of putting a matter to a revealing test.
nounA blue coloring matter traditionally obtained from lichens, used to test whether solutions are acidic or alkaline; by extension, a revealing or decisive test of character, quality, or suitability.
- A blue coloring matter traditionally obtained from lichens, used to indicate whether a solution is acidic or alkaline.
- A decisive or revealing test of someone's character, a product's quality, or a decision's suitability.
"The final interview is often the litmus test for a candidate's readiness for the role."
"The final interview is often the litmus test for a candidate's readiness for the role."
"Immerse the litmus paper in the solution and observe whether it turns red or blue."
The literal dye is generally uncountable. Countable figurative uses are commonly pluralized as “litmus tests.”
"Several litmus tests revealed clear differences in the candidates' technical knowledge."
Its colors turn a chemistry lesson into a verdict: red says acid, blue says base.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does litmus come from?
The word entered English in the 17th century as a term for a blue dye derived from lichens, through Medieval Latin and Modern Latin litmus. The Latin name underlies later expressions such as litmus paper and litmus test. The deeper etymology of the Latin form is uncertain, so claims deriving it from a particular Greek or other source should be treated cautiously.
How litmus is actually used
Modern usage is predominantly figurative and suggests a particularly revealing standard. It is generally neutral but can imply that the test is sharply discriminating or even harsh. The literal chemical meaning remains common in laboratory and educational contexts.