Litmus (noun)

1. A dye obtained from certain lichens, used as an acid-base indicator.
2. A test for determining acidity or alkalinity.
3. A piece of litmus paper used for testing pH.

Origin:

Derived from the middle english word "litmus" and old english "litmæsse" which is the name of a lichen used to make a dye for textiles, it is also used to test the acidity of a solution.

Examples:

1. The litmus test turned red, indicating an acidic solution.
2. The students used litmus paper to test the pH of different liquids.
3. Litmus is used as an indicator in acid-base titrations.
4. The scientist used litmus as a way to test the acidity of a sample.
5. The litmus test is a simple way to determine if a solution is acidic or alkaline.