Acid-base indicator and Litmus

Acid-base indicator noun - An indicator that changes color on going from acidic to basic solutions.

Litmus and acid-base indicator are semantically related. In some cases you can replace term "Litmus" with "Acid-base indicator", this terms are similar.

Litmus 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.

Acid-base indicator and litmus are semantically related. You can use "Acid-base indicator" instead a noun "Litmus".