clean up vs litter

clean up

verb
  • To make an area or a thing clean; to pick up a mess; to tidy. 

  • To make a large profit; to win by a large margin, or to win a large amount, especially in gambling. Also clean house. 

  • To intervene in a fight between two players at low health and easily kill both of them or the winner. 

  • To become clean, handsome, smart in appearance, e.g. for a special occasion, especially when it is out of character to be seen as such. 

litter

verb
  • To drop or throw trash without properly disposing of it (as discarding in public areas rather than trash receptacles). 

  • To give birth to, used of animals. 

  • To strew (a place) with scattered articles. 

  • To supply (cattle etc.) with litter; to cover with litter, as the floor of a stall. 

  • To scatter carelessly about. 

  • To be supplied with litter as bedding; to sleep or make one's bed in litter. 

  • To produce a litter of young. 

noun
  • Material used as bedding for animals. 

  • A platform mounted on two shafts, or a more elaborate construction, designed to be carried by two (or more) people to transport one (in luxury models sometimes more) third person(s) or (occasionally in the elaborate version) a cargo, such as a religious idol. 

  • Collectively, items discarded on the ground. 

  • A covering of straw for plants. 

  • Absorbent material used in an animal's litter tray 

  • The offspring of a mammal born in one birth. 

  • Layer of fallen leaves and similar organic matter in a forest floor. 

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