A female supernatural being who lurks beneath the surface of weed-covered ponds and ditches, waiting to pull in and drown those who venture into or near the water.

1872   C. Hardwick Trad., Superstitions, & Folk-lore xiv. 279   I firmly believed that, if I disobeyed this instruction, a certain water ‘boggart’ named ‘Jenny Greenteeth’ would drag me beneath her verdant screen and subject me to other tortures besides death by drowning.

1931   A. Uttley Country Child iv. 47   She was warned against going near the pretty mill pond..for Jinny Green-teeth lived there, just under the bright green scum.

1980   D. Wakeham in Folklore (1983) 94 248   Ginny Greenteeth..enticed little children into the ponds by making them look like grass and safe to walk on.

   2. Any of various free-floating aquatic plants or algae which grow in ponds and stagnant water, forming colonies that cover the surface of the water, esp. the common duckweed, Lemna minor.

1904   Notes & Queries 7 May 365/2   At this day in all East Lancashire the older inhabitants call the green moss which covers the surface of stagnant ponds ‘Jenny Greenteeth’.

1970   T. Whittle Plant Hunters 257   Duckweed..is less rich in equivalents than most English natives, but it still has ten, among them boggart creed, jenny green-teeth, duck’s meat and toad spit.