Definitions:

1. a coloring material, which is obtained from lichens, that turns red in acidic solutions and blue in alkaline solutions noun
   • We performed a litmus test in chemistry and discovered that the mystery solution was acidic based on the red color of the litmus.
2. a test that relies on a single indicator noun
   • Their litmus test for a good friend was based on timeliness.

Synonyms:

• litmus