Definition of "turnsole"

A heliotrope; so named because its flowers are supposed to turn toward the sun.  examples

A sunflower.  examples

A sun spurge (Euphorbia helioscopia).  examples

The euphorbiaceous plant Chrozophora tinctoria.  examples

A purple dye obtained from Chrozophora tinctoria.  examples

(chemistry, obsolete) litmus