litmus Meaning, Definition & Usage

noun a coloring material (obtained from lichens) that turns red in acid solutions and blue in alkaline solutions; used as a very rough acid-base indicator
litmus test.

D. lakmoes; lak lacker + moes a thick preparation of fruit, pap, prob. akin to E. meat: cf. G. lackmus. See Lac a resinous substance.

(Chem.) 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. ✍ Litmus is used as a dye, and being turned red by acids and restored to its blue color by alkalies, is a common indicator or test for acidity and alkalinity. litmus test, (Fig.) a test for a single factor, which has only two outcomes, positive or negative; (Politics) For voters concerned predominantly by a single issue, the question of whether a candidate is for or against their position on that issue.