keep up vs loiter

keep up

verb
  • To stay even or ahead. 

  • To continue with (work, etc). 

  • To maintain; to preserve; to prevent from deteriorating. 

  • To ensure that one remains well-informed about something. 

  • To prevent someone from going to bed or to sleep 

loiter

verb
  • To remain at a certain place instead of moving on. 

  • To stand about without any aim or purpose; to stand about idly. 

  • For an aircraft to remain in the air near a target. 

noun
  • A standing or strolling about without any aim or purpose. 

How often have the words keep up and loiter occurred in a corpus of books? (source: Google Ngram Viewer )