Origin of litmusOld Norse litmose, lichen used in dyeing ; from litr, color (akin to Gothic wlits, face ; from Indo-European an unverified form wtu-, appearance ; from base an unverified form wel-, to see from source Classical Latin voltus, expression, Welsh gweled, to see) + mosi, moss
Origin of litmusMiddle English litemose (of Scandinavian origin; akin to Old Norse litmosi, dyer's herbs litr, color, dye + mosi, bog, moss) and Middle English lykemose (from Middle Dutch lijkmoes, variant of lēcmoes : lēken, to drip + moes, moss).
(countable and uncountable, plural litmuses)
1495, earlier lytmos, from Old Norse litmosi (“moss used for dyeing”), from lita (“to dye, stain”), from litr (“colour, dye, blee”), from Proto-Germanic *wlitiz, *wlituz (“appearance, blee”), from Proto-Indo-European *wel- (“to see”) + mosi (“moss”). Cognate with Old English wlite (“appearance, form, brightness, countenance”). More at moss.