Litmus is paper that turns red in acid and blue in alkali. Litmus paper, test with litmus, a litmus test.
The dye comes from lichens, and the test is crude but instant. A litmus test in politics is a single question used to sort people into camps, and the metaphor is apt: it gives one bit of information and nothing about degree.
1nounlitmusPaper that turns red in acid and blue in alkali.
“The students dipped strips of litmus into each liquid to see which were acids.”
litmus is a test material.
Old Norse litmosi means dye moss, from litr, colour, plus mosi, moss.
Proto-Indo-European
*wel- — to see
Proto-Germanic
*wlitiz
Old Norse
litmosi — moss used for dyeing
Middle English
litmose
English, today
litmus
Built from
From Middle English litmose, lytmose, litemose, from Old Norse litmosi (“moss used for dyeing”), from lita + mosi, the former from litr (“colour, dye, blee”), from Proto-Germanic wlitiz, wlituz (“appearance, blee”), from Proto-Indo-European wel- (“to see”). Cognate with Old English wlite (“appearance, form, brightness, countenance”). More at moss.
Etymology from Wiktionary, CC BY-SA