litmus
UK[ˈlɪtməs]US[ˈlɪtməs]
n
A substance obtained from lichens that turns red in acid solutions and blue in alkaline solutions, used as a chemical indicator.
Etymology
The word 'litmus' entered Middle English from Old Norse, reflecting the practical knowledge of Scandinavian cultures in using natural resources. Its original form, 'litmosi', literally meant 'dye-moss', directly naming the lichens from which the coloring substance was extracted. This term was adopted into the language of medieval science and trade, preserving its reference to the organic source material. Over centuries, its application narrowed specifically to the chemically reactive dye used as a pH indicator, while the original compound meaning of 'coloring moss' faded from general use.
Analysis
The word is a simplex loanword. It originates from Old Norse 'litmosi', meaning 'dye-moss' or 'lichen for dyeing', where 'litr' means 'color, dye' and 'mosi' means 'moss'.
Examples
The scientist dipped the paper in litmus to test the liquid's pH.
Litmus paper is a common tool in chemistry classrooms.
The decision acted as a litmus test for the government's true intentions.