litmus
noun /ˈlɪtməs/
/ˈlɪtməs/
[uncountable]- a substance that turns red when it touches an acid and blue when it touches an alkali
- litmus paper
Oxford Collocations DictionaryLitmus is used before these nouns:- paper
Word OriginMiddle English: from Old Norse lit-mosi, from litr ‘dye’ + mosi ‘moss’.