ˈlitməs noun
( -es )
Etymology: of Scandinavian origin; akin to Old Norse litmosi herbs used in dyeing, from litr color + mosi moss; akin to Old English wlite face, Old High German ant lizzi face, Old Norse līta to look, Gothic wlits face, figure, wlaiton to spy, look, Latin voltus, vultus facial expression, appearance, face, Middle Welsh gwelet to see — more at moss
: a coloring matter that turns red in acid solutions and blue in alkaline solutions, is obtained from several lichens (as Roccella tinctoria, R. fuciformis, or Lecanora tartarea ), is usually formed with powdered chalk or gypsum into small blue cakes, and is used as an acid-base indicator — compare archil , azolitmin