lie-in vs picket line

lie-in

noun
  • A form of protest where a group of people lie down in a public area. 

  • A period spent lying in bed for longer than usual after one has woken up. 

picket line

noun
  • A boundary guarded by a picket (unit of soldiers). 

  • A barrier or fortification formed by pickets; a stockade. 

  • A boundary created by workers participating in a strike, generally at the workplace entrance, which other workers are asked not to pass. 

  • A line or rope held by one or many pickets, chiefly one used for tethering horses. 

How often have the words lie-in and picket line occurred in a corpus of books? (source: Google Ngram Viewer )