Litmus
WordNet
noun
(1) 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
WiktionaryText
Noun
- A dyestuff extracted from certain lichens, that changes color when exposed to pH levels greater than or less than certain critical levels.
- A simple test of acidity in a liquid using litmus, usually in the form of litmus paper.
- A simple test of any attribute; a litmus test.