bittern

Etymology 1

From Middle English bitour, botor, from Old French butor, from Gallo-Roman *butitaurus, a blend of Latin būtiō (“bittern”) and taurus (“bull, ox”).

noun

1. Several bird species in the Botaurinae subfamily of the heron family Ardeidae.
   It is a great rock or cliff on the loneliest part of the mountains, and […] is known by the name of the Garden Rock. Near the foot of it is a small lake, the haunt of the solitary bittern, with water-snakes basking in the sun on the leaves of the pond-lilies which lie on the surface. 1819, Washington Irving, The Sketch Book, Rip Van Winkle

Etymology 2

From bitter with an unclear suffix, perhaps a dialect form of -ing.

noun

1. The liquor remaining after halite (common salt) has been harvested from saline water (brine).
2. The saline substance added to soy milk to coagulate it as a primary step in the production of tofu.
   Now we add the bittern. 2019, “The Secrets of Tofu across Japan”, in Seasoning the Seasons, NHK World-Japan
3. (archaic) A very bitter compound of quassia, cocculus indicus, etc., used by fraudulent brewers in adulterating beer.