stop up

present singular third person stops up · participle present stopping up · participle past stopped up · past stopped up

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

   So then we […] scratched around and found an old tin washpan, and stopped up the holes as well as we could.

   1885, Mark Twain, chapter 37, in Huckleberry Finn

2. UKlawTo permanently close or block (a road or path); to legally extinguish a right of way.
3. artsTo 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 stop down means to narrow the aperture; to stop up or open up means to expand it.

   2002, Kathleen Tracy, The Complete Idiot's Guide to Portrait Photography, →ISBN, page 18