impound vs pen in

impound

verb
  • To shut up or place in an enclosure called a pound. 

  • To hold back. 

  • To collect and hold (funds) for payment of property taxes and insurance on property in which one has a security interest. 

  • To hold in the custody of a court or its delegate. 

noun
  • A place in which impounded things are stored. 

  • That which has been impounded. 

  • The state of being impounded. 

  • Amounts collected from a debtor and held by one with a security interest in property for payment of property taxes and insurance. 

pen in

verb
  • To enclose (animals) in a pen. 

  • To schedule; fix a date for. 

  • To cause to be stuck in a situation; to be forced into a situation by circumstances. 

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