lemon vs yellow light

lemon

noun
  • A more or less bright shade of yellow associated with lemon fruits. 

  • A semitropical evergreen tree, Citrus limon, that bears such fruits. 

  • A defective or inadequate item or individual. 

  • A yellowish citrus fruit. 

  • Favor. 

  • A piece of fanfiction involving explicit sex. 

adj
  • Containing or having the flavour/flavor and/or scent of lemons. 

  • Of the pale yellow colour/color of lemons. 

  • Smart; cheeky, vocal. 

verb
  • To flavour with lemon. 

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 lemon and yellow light occurred in a corpus of books? (source: Google Ngram Viewer )