LITMUS Meaning of LITMUS in English [ 'lɪtməs ]■ noun a dye obtained from certain lichens that is red under acid conditions and blue under alkaline conditions.OriginME: from ON lit-mosi , from litr 'dye' + mosi 'moss'. Concise Oxford English vocab. Сжатый оксфордский словарь английского языка. 2004