1. a dye obtained from lichens that turns red in acidic solutions and blue in alkaline solutions, used as an indicator in chemistry
Usage: chemistry
2. a test or criterion for determining the true nature or quality of something
Usage: figurative

Examples

• The student dipped litmus paper into the solution to test its acidity.
• Red litmus paper turns blue when placed in a basic solution.
• The chemistry lab was stocked with litmus strips for pH testing.
• His reaction to criticism became a litmus test for his character.
• The candidate’s stance on education served as a litmus test for voters.
• Environmental policy is often used as a litmus test for political parties.