The Collaborative International Dictionary
Turnsole \Turn"sole`\, n. [F. tournesol, It. tornasole; tornare to turn (LL. tornare) + sole the sun, L. sol. See Turn, Solar, a., and cf. Heliotrope.] [Written also turnsol.]
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(Bot.)
A plant of the genus Heliotropium; heliotrope; -- so named because its flowers are supposed to turn toward the sun.
The sunflower.
A kind of spurge ( Euphorbia Helioscopia).
The euphorbiaceous plant Chrozophora tinctoria.
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(Chem.)
Litmus. [Obs.]
A purple dye obtained from the plant turnsole. See def. 1 (d) .
Wikipedia
Chrozophora tinctoria (commonly known as dyer's croton, giradol, or turnsole) is a plant species native to the Mediterranean, the Middle East, India, Pakistan, and Central Asia.
Chrozophora tinctoria produced the blue-purple colorant " turnsole" used in medieval illuminated manuscripts and as a food colorant.