litmus
‘coloring matter that turns red in acid solution and blue in alkaline solution’
Lexical development traced from the Tamil root:
E. lyȝtmose, litmouce, litt(i)mus, litmose, lytmus < Norw. litmose (< O.Nor. lita ‘to dye, to stain’ + mos ‘moss’), said to be in part from M.Du. lijkmoes (lac < F. lacce < lacca < Med.Lat. lacca < Pers. Lak < Hin. lakh < Skt. laksha ‘red dye’ + moes ‘pulp’) < lit < arakku ‘resin’ < Tamil ar