henna vs yellow light

henna

noun
  • A reddish plant substance, prepared from the dried leaves of this plant, used for temporary tattoos and hair coloring. Hair colorings range from bright red to earth brown to near black. 

  • A shrub, Lawsonia inermis, having fragrant reddish flowers 

  • A rich reddish-brown colour. 

adj
  • Of a rich reddish-brown colour. 

verb
  • To dye or tattoo with henna. 

yellow light

noun
  • Used other than figuratively or idiomatically: see yellow, light. 

  • A traffic light, between the green light and the red light, indicating that vehicles should stop if safely possible. 

  • Hesitance to proceed; limited approval or permission to proceed. 

How often have the words henna and yellow light occurred in a corpus of books? (source: Google Ngram Viewer )