stop up vs unstop

stop up

verb
  • To permanently close or block (a road or path); to legally extinguish a right of way. 

  • To increase the aperture of a photographic lens, moving from an f/stop represented by a higher number to an f/stop represented by a lower number and causing more light to pass into the camera. 

  • To fill a hole or cavity, or block (an opening or passage), as with a plug. 

unstop

verb
  • To draw out the stops of (an organ). 

  • To remove a stoppage; to clear a blockage. 

  • To unplug or uncork a container. 

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