litmus

(litməs)

noun

a purple coloring matter obtained from various lichens and used as an acid-base indicator in chemical analysis: it turns blue in bases and red in acids

Origin: ON litmose, lichen used in dyeing < litr, color (akin to Goth wlits, face < IE *wtu-, appearance < base *wel-, to see > L voltus, expression, Welsh gweled, to see) + mosi, moss

See litmus in American Heritage Dictionary 4

noun
A water-soluble blue powder derived from certain lichens that changes to red with increasing acidity and to blue with increasing basicity.

Origin:

Origin: Middle English litemose (of Scandinavian origin; akin to Old Norse litmosi, dyer's herbs litr, color, dye + mosi, bog, moss)

Origin: and Middle English lykemose (from Middle Dutch lijkmoes, variant of lēcmoes : lēken, to drip + moes, moss)

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