[lit-muh
s] 
| a blue coloring matter obtained from certain lichens, esp. Roccella tinctoria. In alkaline solution litmus turns blue, in acid solution, red: widely used as a chemical indicator. |
| lit·mus (lĭt'məs) n. A water-soluble blue powder derived from certain lichens that changes to red with increasing acidity and to blue with increasing basicity. [Middle English litemose (of Scandinavian origin; akin to Old Norse litmosi, dyer's herbs litr, color, dye + mosi, bog, moss) and Middle English lykemose (from Middle Dutch lijkmoes, variant of lēcmoes : lēken, to drip + moes, moss).] |
In chemistry, a kind of paper used to tell whether a solution is an acid or a base. Acids turn blue litmus paper red; bases turn red litmus paper blue. Other testing paper or sophisticated instruments can be used to measure the pH of a solution more precisely.
Note: The term litmus is often used to refer to a general and simple test: “Your vote on this issue is a litmus test of your political philosophy.”
litmus lit·mus (lĭt'məs)
n.
A water-soluble blue powder derived from lichens that changes to red with increasing acidity and to blue with increasing basicity.