stop up


  1. To fill a hole or cavity, or block an opening or passage, as with a plug.
  2. 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.

The above text is a snippet from Wiktionary: stop up
and as such is available under the Creative Commons Attribution/Share-Alike License.

Need help with a clue?
Try your search in the crossword dictionary!